LIGO/Virgo G298048, GRB 170817A, LIGO/Virgo GW170817

D. Dobie (University of Sydney), K. Mooley (Caltech),
T. Murphy (University of Sydney), D. Kaplan (UWM), E. Lenc (CSIRO),
A. Corsi (TTU), D. Frail (NRAO), report on behalf of a larger collaboration
Our continued observations of GW170817 with the ATCA and the VLA up to 300
days post-merger (Mooley et al. in prep) confirm the t^(-2) decline in the
radio light curve initially reported in Mooley et al. 2018 (arXiv:1806.09693
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 ).
Such a slope rules out a cocoon-dominated outflow at late times, and is
instead the classic signature of a relativistic jet, consistent with the
VLBI result from Mooley et al. 2018. The t^(-2) decline is also expected in
the X-ray light curve, and may be confirmed by the Chandra observation carried
out on 2018 Aug 10.

A. Rossi (INAF-OAS),  M. Cantiello (INAF-OA Abruzzo) V. Testa, D. Paris 
(INAF-OAR), A. Melandri, S. Covino,  O. S. Salafia, P. D'Avanzo, S. 
Campana (INAF-OAB), L. Nicastro, E. Palazzi, F. Cusano (INAF-OAS), G. 
Stratta (Urbino University/INFN Firenze), R. Carini, S. Piranomonte, E. 
Brocato (INAF-OAR), V. D'Elia (ASDC), and M. Branchesi (GSSI) report on 
behalf of the GRAWITA collaboration and its partners:

We observed the optical counterpart of GRB 170817A (Kienlin et al., GCN 
21520
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 ) associated to GW 170817 (LVC GCN Circ. 21509
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 , 21513
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 ) with the LBC 
imager mounted on the Large Binocular Telescope (Mt Graham, AZ, USA). 
Observations were performed in the r-sloan filter on 2018-01-23, i.e., 
~160 days after the GW/GRB trigger.

At the location of the optical transient (e.g., Coulter et al., GCN 
21529
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 ; Adams et al., 21816) we detect the optical afterglow of GRB 
170817A with magnitude r-sloan=26.2+-0.4, calibrated against Pan-STARRS 
field stars. Image analysis was performed after preliminary removal of 
an elliptical model of the underlying host galaxy from each single 
frame. However, some residual emission is left which contributes for 
~0.2 mags to the uncertainty of the photometry.

Our detection is the first one from a ground-based optical telescope. It 
is in agreement with a turnover/flattening in the optical light curve of 
GW 170817/GRB 170817A as inferred by Alexander at al. 2018 
(arXiv:1805.02870
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 ) and with the overall flattening/declining temporal 
evolution observed in the X-ray and radio bands (D'Avanzo et al. 2018, 
A&A, 613 L1; Hajela et al. GCN Circ. 22692
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 ; Troja et al. GCN Circ. 
22693
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 ; Dobie et al. arXiv:1803.06853
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 ; Alexander at al. 2018; 
arXiv:1805.02870
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 ).

We acknowledge the excellent support from the LBT staff in obtaining 
these observations.

E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of
a larger collaboration:

We analyzed the full set of five observations of GW170817
performed by the Chandra X-ray Observatory between January 17th
and January 28th, 2018, i.e. ~153 and ~164 days after the merger.
A log of observations is reported below:

ObsID     Exposure [ks]   0.5-8.0 keV count rate [cts/s]

20936     31.75           0.0018 +/- 0.0002
20937     20.77           0.0014 +/- 0.0003
20938     15.86           0.0019 +/- 0.0003
20939     22.25           0.0011 +/- 0.0002
20945     14.22           0.0010 +/- 0.0003

The average net count-rate is 0.00148 +/- 0.00011 cts/s,
consistent with the value of 0.00145 +/- 0.00014 observed
at 110 days (Troja et al. 2018, arXiv:1801.06516
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 ).
The average spectrum, obtained by coadding the five exposures,
is well described by an absorbed power-law model with
N_H=7.5E20 cm^-2 and photon index Gamma=1.65+/-0.16 (68% c.l.),
consistent with the value derived from the broadband spectrum
at earlier times (Troja et al. 2018, arXiv:1801.06516
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 ).
Based on this new analysis, we estimate an unabsorbed X-ray flux
of (2.6 +/- 0.3)E-14 erg/cm2/s (68% c.l.) in the 0.3-10 keV band,
consistent with the X-ray flux measured at 110 days.

Our results do not support the claim of a decreasing X-ray flux,
as suggested by D'Avanzo et al. (2018, arXiv:1801.06164
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 ), and
are consistent either with a slowly rising afterglow or a slow
turn-over of the X-ray light curve expected when the afterglow
reaches its peak (e.g. Lazzati et al. 2017, arXiv:1712.03237
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 ;
Troja et al. 2018, arXiv:1801.06516
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 ).

We note that the X-ray afterglow displays a marginal level of
variability on timescales of a few days, being the count-rate
from the last two exposures (20939,20945) consistently lower.
The spectrum from these two observations is characterized by a
photon index Gamma= 1.9 +/- 0.3 (68% c. l.), slightly softer
than the value measured in the first three exposures (20936,20937,
and 20938) Gamma = 1.59+/-0.17 (68% c. l.), yet consistent within
the large uncertainties. The lower count-rate and soft spectral
shape could be indicative of the cooling frequency entering the
X-ray band, although the limited statistics prevent us to draw
any firm conclusion.

E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of
a larger collaboration:

The Chandra X-ray Observatory re-observed the field of GW170817
starting on January 17th, 2018, and performed five short exposures
observations as part of its on-going monitoring program (PI: Wilkes).

Only three of these exposures (ObsID: 20936, 20938, 20939) are currently
archived and available to the public. Here we report the preliminary 
findings
from these observations.

The X-ray afterglow is detected with high significance in all the exposures
at an average count rate of 0.0016 cts/s in the 0.5-8.0 keV energy band.
A preliminary inspection of the hardness ratio does not show any 
significant
spectral variation. Therefore, we perform a spectral analysis using an 
absorbed
power-law model with absorption column fixed at the Galactic value of
7.5E20 cm^-2 and a photon index Gamma=1.575 as derived from our broadband
analysis (Troja et al. 2018, arXiv:1801.06516
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 ).

We derive an unabsorbed X-ray flux of (3.2 +/- 0.3)E-14 erg/cm2/s in the
0.3-10 keV energy band. The quoted error is at the 68% confidence level.
This new measurement is higher than the value measured by Chandra
at ~110 days (~2.5E-14 erg/cm2/s, Troja et al. 2018), and higher than the
value measured by XMM-Newton at ~135 days (D'Avanzo et al., 2018).

The latest measurement is consistent with a rising afterglow with F~t^0.8,
although, within the errors, a slow turn-over of the X-ray light curve
cannot be excluded.

Further analysis is on-going.

Daryl Haggard, Melania Nynka, John J. Ruan (McGill/MSI), Phil Evans 
(Leicester), and Vicky Kalogera (Northwestern/CIERA) report:

We have obtained new X-ray observations of GW170817 via Chandra 
Director's Discretionary Time (PI: Wilkes, Program Number 19408607). The 
X-ray counterpart to GW170817/GRB170817A/SSS17a continues to be detected 
and the X-ray emission continues to brighten approximately 156 days 
after the neutron star merger. This contradicts previous claims of the 
X-ray fading of GW170817 in XMM-Newton observations at 135 days 
(D'Avanzo et al. 2018, arXiv: 1801.06164).

This new Chandra program acquired several exposures of GRB170817A:

ObsID,  ExpTime,  StartDate,           Days Post-Burst
-----   -------   ---------            ---------------
20936   31.75 ks  2018-01-17 21:55:17  153.5 days
20938   15.86 ks  2018-01-21 13:45:18  157.1 days
20939   22.25 ks  2018-01-24 08:18:48  159.9 days

Since these new Chandra exposures are close in time and the X-ray 
emission of GRB170817A is not expected to vary significantly over <10 
day timescales, we co-add these three data sets into one 69.86 ks 
exposure at 156.4 days post-burst.

We perform spectral extractions assuming an absorbed power-law spectral 
model with fixed NH = 7.5e20 cm^���2 and find that the X-ray flux of 
GRB170817A has an absorbed flux of f(0.3���8 keV) = 1.93(+0.39/-0.32)e���14 
erg s^���1 cm^���2  (with Gamma ~ 1.67) at 156.4 days post-burst, which 
corresponds to an unabsorbed luminosity of L(0.3���10 keV) = 
5.23(+1.30/-0.95)e39 erg s^���1 (assuming a luminosity distance of 42.5 Mpc).

This represents continued X-ray brightening compared to Chandra 
observations at 15.6 and 109.2 days post-burst, for which we find an 
absorbed flux of f(0.3���8 keV) = 0.36(+0.1/-0.07)e���14 erg s^���1 cm^���2 
(with Gamma = 2.4 +/- 0.8, unabsorbed L(0.3���10 keV) = 10.4(+2.0/-1.6)e38 
erg s^���1; Haggard et al. 2017) and f(0.3���8 keV) = 1.58(+0.14/-0.13)e���14 
erg s^���1 cm^���2 (with Gamma = 1.6 +/- 0.3, unabsorbed L(0.3���10 keV) = 
42.5(+3.7/-3.5)e38 erg s^���1; Ruan et al. 2018), respectively.

Our findings here contradict recent reports of dimming in the X-ray flux 
from XMM Newton at 135 days (D'Avanzo et al. 2018), which was reported 
to be 2.1(+0.7/-0.5)e-15 erg s^���1 cm^���2 (0.3-10 keV unabsorbed). 
However, this reported flux value is a typo, and should be 
2.1(+0.7/-0.5)e-14 erg s^���1 cm^���2 (D���Avanzo 2018, private 
communication). Taking this corrected flux and rescaling to a 0.3-8 keV 
absorbed flux for comparison to the previous Chandra measurements above 
gives 1.67(+0.87/-0.64)e-14 erg s^���1 cm^���2. Thus, the recent X-ray data 
at 15.6 days (Chandra), 109.2 days (Chandra), 135 days (XMM), and 156.4 
days (Chandra) are all consistent with continued X-ray brightening. We 
provide a light curve table summarizing these measurements:

Days,  Telescope,  Flux* (0.3-8 abs),     Ref
----   ---------   ----------------       ---
15.6   Chandra     0.36(+0.10/-0.07)e���14  Haggard et al. (2017)
109.2  Chandra     1.58(+0.14/-0.13)e���14  Ruan et al. (2018)		
135    XMM         1.67(+0.87/-0.64)e-14  D'Avanzo et al. (2018)	
156.4  Chandra     1.93(+0.39/-0.32)e-14  This work

*Flux units: erg s^���1 cm^���2; all uncertainties are 90% confidence interval

Current post-merger models suggest that the origin of the X-rays could 
be afterglow emission from either a mildly-relativistic cocoon or a 
structured jet. For a cocoon, the continued rise of X-ray emission 
suggest that the cocoon has not yet reached a deceleration phase. For a 
structured jet, the rising X-ray emission suggest emission from the jet 
core has not yet entered the observed line of sight. Continued 
monitoring of GW170817 will be critical for discriminating between these 
and other models.

Note that another ~30 ks of Chandra observations during this same time 
interval are forthcoming.

We thank Belinda Wilkes and the Chandra scheduling, data processing, and 
archive teams for making these observations possible.

A. Grado (INAF-OAC), E. Cappellaro (INAF-OAPD), F. Getman (INAF-OAC), L.
Limatola (INAF-OAC), S. Yang (INAF-OAPD), M. Branchesi (GSSI), S. Covino
(INAF-OAB), P. D'Avanzo (INAF-OAB),  M. Della Valle (INAF-OAC), A. Melandri
(INAF-OAB), L. Amati (INAF-OAS), S. Ascenzi (INAF-OAR), S. Benetti
(INAF-OAPD), M.T. Botticella (INAF-OAC), G. Greco (Urbino University/INFN
Firenze), L. Nicastro (INAF-OAS), E. Palazzi (INAF-OAS), E. Pian
(INAF-OAS), S. Piranomonte (INAF-OAR), A. Rossi (INAF-OAS), G. Stratta
(Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), L . Tomasella
(INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf
TeAm.

Observations pointed at the position of AT2017gfo
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  of the skymap of the
Advanced LIGO and Virgo trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) using
the VLT Survey Telescope (VST - Proposal ID ESO 0100.D-0022) at ESO-Paranal
equipped with OMEGACAM (FOV=1 square degree). The images were acquired with
the g_SDSS, r_SDSS, filters for a total exposure of 5400s in each band. The
observations were executed in the nights 2018-01-05, 2018-01-18 and
2018-01-19, starting at 2018-01-05T 06:57:00.057 UTC and finishing at
2018-01-19T 06:55:22.862 UTC. The median FWHM and the 50% completeness
magnitudes are 0.91", 0.92" and 25.0  and 24.5 AB mags for the g_ssds and
r_sdss bands respectively.
No source is visible at the GW optical counterpart coordinates
RA=13:09:48.09 DEC=-23:22:53.35.
We acknowledge excellent support from the ESO User Support Department and
from ESO observing staff in Paranal.

K. P. Mooley (Oxford, NRAO/Caltech) et al. report

The X-ray flux of GW170817 on December 03-06 (reported by Troja et al. 
2017, GCN 22201
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 ; Margutti et al. 2017, GCN 22203
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 , Haggard et al. 2017, 
GCN 22206
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  based on the Chandra observations) is exactly as predicted 
last week by Mooley et al. 2017 (http://arxiv.org/abs/1711.11573
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 ) based 
on radio spectral indices.

This suggests that the radio and X-ray emission both arise from a mildly 
relativistic wide-angle outflow, consistent with the cocoon model (see 
also Gottlieb et al. 2017, Hallinan et al. 2017, Kasliwal et al. 2017). 
A relativistic jet core, if it exists, is either too weak (having a 
sub-dominant contribution to the radio light curve early on) or too 
strong (such that its electromagnetic signatures will be observed in the 
future). See Mooley et al. 2017 for details.

A.J. Levan, J.D. Lyman (U. Warwick), N.R. Tanvir (U. Leicester), I. Mandel (U. Birmingham), J. Hjorth (DARK/NBI), A.S. Fruchter, T. Kangas (STScI), B. Gompertz, K. Wiersema, D. Steeghs (U. Warwick), S. Rosswog (Stockholm) report on behalf of a larger collaboration: 

"We obtained further observations of the counterpart of GW170817 with the Hubble Space Telescope. Observations took place on 6 Dec 2017 and utilised both optical (F606W, F814W) and infrared (F140W,F160W) filters. 

At the location of the transient we recover the source in both optical filters, but do not detect it in the infrared, where the background from the galaxy is higher. The measured magnitudes of the source in the optical bands are broadly consistent with the extrapolation from the 93 day radio epoch (Mooley et al. 2017 arXiv 1711.11573) to the near contemporaneous observations with Chandra (Troja et al. 2017 GCN 22201
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 , Margutti et al. 2017 GCN 22202
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 ). 

We thank the staff of STScI for their excellent support with these observations."

Daryl Haggard, John J. Ruan, Melania Nynka (McGill/MSI), Vicky Kalogera (Northwestern/CIERA), and Phil Evans (Leicester) report:

We have performed a detailed analysis of new Chandra X-ray observations of GW170817 obtained via Chandra Director's Discretionary Time (PI: Wilkes, Program Number 18408601). The X-ray counterpart to GW170817/GRB170817A/SSS17a is clearly detected in the new observations.

This program acquired two exposures of GRB170817A: (1) a 74.09 ks exposure (ObsID 20860) beginning at 2017 December 2.08 UT, approximately 108 days post-burst, and (2) a 24.74 ks exposure (ObsID 20861) beginning at 2017 December 6.45 UT, approximately 111 days post-burst. Since the two new exposures are close in time and the X-ray emission of GRB170817A is not expected to vary significantly over ~4 day timescales, we co-add the two data sets into one 98.83 ks exposure at 109.2 days post-burst.

We perform spectral extractions assuming an absorbed power-law spectral model with fixed NH = 7.5e20 cm^���2 and find that the X-ray flux of GRB170817A has an absorbed flux of f(0.3���8 keV) = 1.58e���14 +/- 0.14 erg s^���1 cm^���2  (Gamma = 1.62 +/- 0.27) at 109.2 days post-burst, which corresponds to an unabsorbed luminosity of L(0.3���10 keV) = 42.5e38 +/- 3.7 erg s^���1 (see also Troja et al. GCN 22201
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  and Margutti et al. GCN 22203
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 ). This represents significant X-ray brightening compared to Chandra observations at 15.6 days post-burst, for which we find an absorbed flux of f(0.3���8 keV) = 0.36e���14 +/- 0.1 erg s^���1 cm^���2 (Gamma = 2.4 +/- 0.8) and an unabsorbed luminosity of L(0.3���10 keV) = 10.4e38 +/- 2.0 erg s^���1 (Haggard et al. 2017).

We also examine the three previously-detected X-ray sources CXOU J130948, CXOU 130946, and the host galaxy NGC 4993. The fluxes of CXOU 130946 and the host-galaxy NGC 4993 are consistent with our previous deep Chandra observations, while CXOU J130948 appears to be variable in X-rays (Margutti et al. 2017; Haggard et al. 2017).

The origin of the X-ray emission from the NS-NS coalescence GW170817/GRB170817A is an important diagnostic for all post-merger interpretations, and different scenarios predict distinct evolution in its X-ray light curve. These observations support scenarios in which the X-ray and radio emission share a common origin, i.e., the X-ray light curve is consistent with outflow models which may be either a cocoon shocked by the jet or dynamical ejecta from the merger. Further deep X-ray monitoring can place powerful constraints on the physical parameters of these models. The X-ray brightening strengthens the argument that simple top-hat jet models are not consistent with the latest observations. However, more advanced models of structured jets with off-axis viewing angles should be pursued and cannot yet be ruled out.

We thank Belinda Wilkes and the Chandra scheduling, data processing, and archive teams for making these observations possible.

R. Margutti, W. Fong (Northwestern), T. Eftekhari, K. Alexander, E. Berger
(Harvard), R. Chornock (Ohio University) report:


���The Chandra X-ray Observatory (CXO) started observing GW170817 on 2017
December 3 at 01:38:45UT for a total of 74.09 ksec (obs ID 20860, PI
Wilkes). At the position of the electromagnetic counterpart, an X-ray
source is clearly detected with a significance of ~33-sigma (RA =
13:09:48.090, Dec = -23:22:52.87, J2000), with a net count-rate of 1.47e-3
cps (0.5-8 keV).

The CXO observed the field for an additional 24.74 ksec starting on 2017
December 6 at 10:43:31UT (obs ID 20861, PI Wilkes). The X-ray source is
still detected with a significance of ~15-sigma with a net count-rate of
1.41e-3 cps (0.5-8 keV).

The joint spectrum can be fit with an absorbed power-law spectral model
with photon index Gamma= 1.50 +\-0.16 (1 sigma c.l.). We find no evidence
for intrinsic neutral hydrogen absorption in addition to the Galactic value
(NH_MW=0.0784e22 cm-2, Kalberla et al., 2005) and place a 3 sigma upper
limit of NHint<0.7e22 cm-2. These properties are consistent with the X-ray
spectral properties of GW170817 at t<15 days inferred by Margutti et al.,
2017 and Troja et al., 2017.

Based on our best fitting spectral parameters, the 0.3-10 keV unabsorbed
flux is

2.3e-14 erg/s/cm^2, indicating a substantial brightening of the X-ray
source during the last ~90 days, in agreement with the results from Troja
et al., GCN 22201
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 . A comparison with radio observations acquired 93 days
since merger (Mooley et al., 2017)  indicates a spectral slope beta~-0.6 of
the Fnu ~nu^-beta spectrum, similar to the radio-to-Xray spectrum of
GW170817 before Sun block (Alexander et al., 2017; Margutti et al., 2017;
Troja et al., 2017; Haggard et al., 2017; Hallinan et al., 2017; Mooley et
al., 2017). This result suggests negligible spectral evolution of GW170817
in the last 90 days, and that the radio and X-ray emission continue to
represent the same emission component.

Based on this spectrum, we expect GW170817 to be detectable at optical-NIR
wavelengths at approximately 26.5 AB magnitude.

We thank Belinda Wilkes and the entire CXO team for approving these DDT
requests and making these observations possible.���

E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD),
H. van Eeerten (U. Bath), T. Sakamoto (AGU), and S. B. Cenko (NASA/GSFC)
report:

The Chandra X-ray Observatory re-observed the field of GW170817/AT2017gfo
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(PI: B. Wilkes) starting on 2017-12-03 (~109 days after the LVC trigger)
for a total exposure of 74 ks. A second shorter observation was performed on
2017-12-06 for a total exposure of 25 ks.

Our preliminary analysis of the data clearly detects the X-ray counterpart
of AT2017gfo
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  at a flux level of ~1.5E-14 erg/cm^2/s (0.5-8.0 keV).
The observed value is three times higher than the flux measured at
earlier times (~5E-15 erg/cm^2/s at 15 days; Troja, E., et al. 2017,
Nature, 551, 71) and implies a continued rise of the X-ray afterglow.
We do not measure any significant spectral variation between these
observations and our observations at earlier times.

This behavior is hard to reconcile with the simple top-hat jet model and
suggests a more complex structure of the GRB jet.


We thank Belinda Wilkes, Andrea Prestwich and the entire Chandra for
performing these observations.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We have re-analysed offline noise-subtracted data for the LIGO Hanford
Observatory (H), LIGO Livingston Observatory (L), and Virgo (V) detectors
around the time of the binary neutron star merger event G298048 / GW170817
(GCNs 21505
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 , 21509
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 , 21510
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 , 21513
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 , 21527
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 ) taking into account our most
up-to-date understanding of both calibration and waveform modelling
uncertainties.

Parameter estimation has been performed using LALInference (Veitch et al.,
PRD 91, 042003) and a new sky map, LALInference_v2.fits.gz, is available
for retrieval from the GraceDB event page:

https://gracedb.ligo.org/events/G298048

The 50% and 90% credible regions span about 8 and 28 square degrees,
respectively.

This is the preferred sky map at this time, and the version that will
appear in LVC 2017 (Physical Review Letters, accepted).

R. M. Lau (Caltech), E. O. Ofek (Weizmann) and M. M. Kasliwal (Caltech)
report on behalf of the Global Relay of Observatories Watching Transients
Happen (GROWTH) collaboration:

On 2017 Sept 29.86 UT, the Spitzer space telescope took deep mid-infrared
observations at the position of SSS17a (Coulter et al. LVC GCN 21529
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 ) with
Channel 1 (3.6 microns) and Channel 2 (4.5 microns) of the  Infrared Array
Camera (IRAC).

We conducted a preliminary analysis of the IRAC Basic Calibrated Data
(BCD), including both a median filter subtraction and ZOGY image
subtraction to remove the extended emission from the host galaxy NGC 4993.
We find possible, marginal evidence for excess emission at the position of
SSS17a at 4.5um. We are continuing monitoring with Spitzer/IRAC.

We thank the Spitzer Space Telescope team, in particular, Tom Soifer and
Nancy Silbermann, for the rapid review and scheduling of these DDT
observations (PI Kasliwal). The Spitzer Space Telescope is operated by the
Jet Propulsion Laboratory, California Institute of Technology under a
contract with NASA.

T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech),
M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U
Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J.
Tsai (Virginia Tech), C. Yancey (U Maryland)

As previously reported (GCN 21680
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 , GCN 21848
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 ), the Long Wavelength
Array (LWA1, located west of Socorro, New Mexico) followed up on
G298048 on 17 August and 24 August, observing with 4 beams: one
centered on NGC 4993, one including it off-center, and two nearby that
exclude the source.

After including observations from an additional epoch (30 August at
19:50 UTC, two weeks after the GW event), and further analysis, we
have concluded that the detection reported earlier (GCN 21848
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 ) is not
statistically significant. We now set 3-sigma upper limits to the
appearance of a radio source in an LWA1 beam centered on NGC 4993,
about 8 hours after the GW event, as ~200 Jy at 25 MHz and ~100 Jy
at 45 MHz.

A publication describing these limits and our analysis is in
preparation.

Javier Moldon, Rob Beswick (JBCA, The University of Manchester) et al.
for the EuroVLBI team

We conducted a total of 22 e-MERLIN observations of SSS17a (Coulter et
al. LVC GCN  21529
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 ) from Aug 23 to Sep 22, 2017 for about 5 hours per
run. The observing frequency was centred at 5 GHz with a bandwidth of
512 MHz. The average synthesized beam size was about 200 mas x 30 mas
at a position angle of about 0 deg. There are no significant
detections in individual runs or in different combinations of adjacent
runs coincident with the position of the transient.

The 3-sigma upper limits in microJy/beam are listed below (first six
runs were already reported in LVC GCN 21804
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 ). UTC date and times refer
to the middle of the experiments:

run00  2017-08-23 15:36:28  110
run01  2017-08-24 15:33:42   90
run02  2017-08-25 15:30:26   97
run03  2017-08-26 15:30:26  112
run04  2017-08-27 15:30:22   87
run05  2017-08-28 15:30:26   82
run06  2017-08-31 15:01:26  109
run07  2017-09-01 15:01:26  114
run08  2017-09-02 15:04:42  144
run09  2017-09-03 15:01:26  166
run10  2017-09-04 15:01:26  147
run11  2017-09-05 15:31:29  162
run12  2017-09-10 14:54:42  126
run13  2017-09-11 14:44:42  151
run14  2017-09-12 14:03:28  113
run15  2017-09-14 13:26:42  147
run16  2017-09-15 14:03:28  106
run17  2017-09-16 14:03:28  118
run18  2017-09-17 14:03:28  111
run19  2017-09-18 14:03:28  111
run20  2017-09-21 14:18:28  132
run21  2017-09-22 13:34:42  121

Additional observations are planned with e-MERLIN to continue the
monitoring of the transient source.


Euro VLBI team members:

Ivan Agudo (IAA Granada)
Tao An (Shanghai Astronomical Observatory)
Philippe Bacon (APC Universite�� Paris Diderot)
Rob Beswick (JBO-Manchester University)
Carolina Casadio (MPIfR-Bonn)
Eric Chassande-Mottin (APC Universite�� Paris Diderot)
Sa��ndor Frey (Konkoly Observatory)
Marcello Giroletti (IRA-INAF)
Peter Jonker (SRON)
Mark Kettenis (JIVE)
Benito Marcote (JIVE)
Javier Moldon (JBO-Manchester University)
Zsolt Paragi (JIVE)
Arpad Szomoru (JIVE)
Huib van Langevelde (JIVE)
Jun Yang (Onsala Space Observatory)

e-MERLIN is a National Facility operated by the University of
Manchester at Jodrell Bank Observatory on behalf of STFC.



-- 
Zsolt Paragi
Head of User Support

Joint Institute for VLBI ERIC (JIVE)    Web:  http://www.jive.eu
Oude Hoogeveensedijk 4                  Phone:  +31 (0)521-596-536
7991 PD  Dwingeloo                        Mobile:  +31 (0)629-034-718
the Netherlands                                Fax:  +31 (0)521-596-539

Zsolt Paragi (JIVE), Jun Yang (OSO), Benito Marcote (JIVE) et al. for the
Euro VLBI team

Continuing our efforts (LVC GCN 20981
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 , 21804
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 ) to detect radio emission from
SSS17a (Coulter et al. LVC GCN  21529
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 ) on milliarcsecond scales, we observed
the transient at 5 GHz with the European VLBI Network between 10:00���14:30 UT
on 20 September 2017. The 5 sigma upper limit around the HST/Gaia position
(Adams, Kasliwal & Blagorodnova, LVC GCN 21816
Loading...
 
 ) is 140 microJy/beam.
Further observations are planned.

Euro VLBI team members:

Ivan Agudo (IAA Granada)
Tao An (Shanghai Astronomical Observatory)
Philippe Bacon (APC Universite�� Paris Diderot)
Rob Beswick (JBO-Manchester University)
Carolina Casadio (MPIfR-Bonn)
Eric Chassande-Mottin (APC Universite�� Paris Diderot)
Sa��ndor Frey (Konkoly Observatory)
Marcello Giroletti (IRA-INAF)
Peter Jonker (SRON)
Mark Kettenis (JIVE)
Benito Marcote (JIVE)
Javier Moldon (JBO-Manchester University)
Zsolt Paragi (JIVE)
Arpad Szomoru (JIVE)
Huib van Langevelde (JIVE)
Jun Yang (Onsala Space Observatory)

The EVN is a joint facility of independent European, African, Asian,
and North American radio astronomy institutes. Scientific results
from data presented in this publication are derived from the following
EVN project code: RP029.



-- 
Zsolt Paragi
Head of User Support

Joint Institute for VLBI ERIC (JIVE)    Web:  http://www.jive.eu
Oude Hoogeveensedijk 4                  Phone:  +31 (0)521-596-536
7991 PD  Dwingeloo                        Mobile:  +31 (0)629-034-718
the Netherlands                                Fax:  +31 (0)521-596-539

K. D. Alexander (Harvard), W. Fong (Northwestern), P. K. G. Williams, E.
Berger (Harvard), and R. Margutti (Northwestern) report:

We report continued radio monitoring of LIGO/VIRGO G298048 with the Karl G.
Jansky Very Large Array (PI: Alexander, Program 17A-231). Our most recent
observations started on 2017 September 25.703 UT, or 39.2 days post-trigger
(LVC et al., GCN 21509
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 ), at a mean frequency of 6 GHz. We clearly detect
the radio counterpart (Hallinan et al., GCN 21929
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 ) at ~5-sigma significance
at a brightness comparable to the limit of our previous VLA observations.
Further observations are planned.

We thank the VLA staff for their assistance in scheduling and executing
these observations.

S. Goedhart (SKA South Africa) reports on behalf of a larger team:

MeerKAT, currently being commissioned, observed the location of SSS17a 
(Coulter et al. 2017, LVC GCN 21529
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 ) in L band between 25-Aug-2017 and 
17-Sep-2017. No radio afterglow is detected, with upper limits provided 
below. We also provide the flux density of the host galaxy NGC4993 for 
each of three epochs. The observations have an effective (unflagged) 
bandwidth of 0.22 GHz spanning 1.30-1.66 GHz, with a center frequency of 
1.48 GHz. Observations done on 25-27 August were reduced together as one 
epoch (E1; mid-point 26 Aug/08:43 UT). The second epoch consists of 
jointly analyzed data collected on 5-6 September (E2; mid-point 6 
Sep/03:22 UT). The third epoch refers to observations done on 17 
September (E3; start time 07:16 UT).

NGC4993 flux densities (1 sigma uncertainties):

E1: 0.56+/-0.04 mJy (synthesized beam 14.5"x7.8")
E2: 0.58+/-0.05 mJy (synthesized beam 11.8"x6.3")
E3: 0.61+/-0.03 mJy (synthesized beam 10.4"x4.8")

SSS17a flux density limits (3 sigma):

E1: <70 uJy
E2: <75 uJy
E3: <60 uJy

We thank the SKA South Africa team for enabling these observations.

T. Batsch, A.J. Castro-Tirado, H. Czyrkowski, A. �wiek, M. �wiok,
R. D�browski, M. Jel�nek, G. Kasprowicz, A.Majcher, K. Ma�ek,
L. Mankiewicz, K. Nawrocki, �. Obara, R. Opiela, L. W. Piotrowski,
M. Siudek, M. Soko�owski, R. Wawrzaszek, G. Wrochna, A. Zadro�ny,
M. Zaremba, A.F. �arnecki (Pi of the Sky Collaboration)

Pi of the Sky robotic wide field of view telescopes search for the
possible EM transients in the sky scans performed twice a night. Each
of the two observation sites (South telescope in Chile and the North
one in Spain) can cover up to about 20000 sq. deg. with range up to
about 12.5m. Dedicated algorithms search for brightness changes of
objects listed in GLADE to detect optical transients that might be
connected with those galaxies.

In the analysis related to G29048 we considered data collected by Pi
of the Sky North telescope located in Spain, near Huelva, between
August 17 and August 21, while the earlier data collected between
August 10 and August 16 were used as a reference. The observations
were performed in wide visible band, with IR-cut and UV-cut filters
only, to achieve deepest detection limit. For each scan field 10
images with 10s exposure were taken and stacked for the analysis. On
the night of 20170817 we surveyed area that overlaped partially with 
the initial bayesstar skymap for G298048. Unfortunatly, the dedicated 
scan procedure was interupted twice that night by the GCN alerts, 
resulting in the event coverage reduced to only about 29% probability, 
even after including other data collected that night. Coverage of 
about 51% was expected for uninterupted scan procedure, as 
obtained on the following nights. Data was searched for any type of 
transients connected with objects from GLADE catalogue. No 
significant transient candidate remained after all selection cuts.

We acknowledge hospitality and support of the INTA El Arenosillo 
Test Centre in Mazag�n near Huelva, Spain.


Fields covered with the sky scan procedure on 20170817
------------------------------------------------------

Pointing (RA[deg],Dec[deg]) gives the center of 20x20 deg^2 FOV.

Field name     Pointing
S0120_10_10   ( 10.8, -0.2)
S0000+50_35   ( 16.9, 57.1)
S0200+50_10   ( 17.7, 39.5)
S0120_10_35   ( 29.4, 18.1)
S0200+50_35   ( 47.0, 57.1)
S0000+90_35   ( 61.0, 77.4)
S1600+50_35   (227.7, 40.7)
S1600+10_10   (230.2,  0.1)
S0000+90_10   (244.6, 76.8)
S1600+10_35   (249.2, 18.0)
S1600+50_10   (257.5, 58.5)
S1840+10_10   (270.4,  0.0)
S2000+50_10   (287.8, 39.5)
S1840+10_35   (289.3, 18.0)
S2120+10_10   (310.6, -0.1)
S2000+50_35   (317.1, 56.9)
S2299+50_10   (317.6, 39.5)
S2120+10_35   (329.4, 18.1)
S2240+10_10   (330.5, -0.1)
S2299+50_35   (347.0, 57.3)
S0000+50_10   (348.0, 39.4)
S2240+10_35   (349.5, 18.2)

Fields covered with other sky observations on 20170817
------------------------------------------------------

GRB170817_35  ( 39.2, 79.9),
GRB170817_10  (250.2, 73.4),
GRB170818_35  (312.4, 10.7),

S0000-10_35   (  9.0, -1.9),
R0000+30_10   ( 11.3, 39.0),
S0200+50_10   ( 17.7, 39.4),
S0326+70_10   ( 33.0, 58.8),
S0326+70_10   ( 33.2, 58.8),
S0200+50_35   ( 47.0, 57.1),
S0326+70_35   ( 89.9, 75.9),
S1440+10_10   (210.2,  0.3),
S1440+10_35   (229.0, 18.2),
S1630+30_10   (236.9, 20.1),
S1630+30_35   (258.5, 38.0),
S2000-10_10   (289.8,-19.8),
S2000-10_35   (308.7, -1.7),
S2120-10_10   (309.8,-19.7),
S2200+50_10   (317.4, 39.4),
S2120-10_35   (328.9, -1.8),
S2240+10_10   (330.4, -0.2),
R0000+30_35   (349.6, 21.0),
S2200+50_35   (346.7, 57.2),
S2240+10_35   (349.3, 18.2),
S0000-10_10   (350.0,-19.8),

This message can be cited.

G. Hallinan (Caltech), A. Corsi (TTU), K. Mooley (Hintze Fellow, 
Oxford), D.A. Frail (NRAO), M.M. Kasliwal (Caltech), report on behalf of 
a larger collaboration:

Our collaboration (GROWTH, JAGWAR, Caltech-NRAO, TTU-NRAO) has continued 
to monitor the evolution of the radio counterpart to GW170817/SSS17a 
discovered on September 2,3, 2017 with the Jansky VLA (Mooley et al. LVC 
GCN 21814
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  and Corsi et al. LVC GCN 21815
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 ), with ongoing observations at 
frequencies of 1.4 GHz, 3 GHz and 6 GHz. Responding to a request for 
further information to help plan observations at other radio facilities, 
we are including details on the most recent detection at 3 GHz, wherein 
the source was detected at a flux density of 34 +/- 3.6 uJy on Sept 17 
(UT). The full light curves and interpretation have been submitted for 
publication (Hallinan, Corsi et al.).

We thank the VLA staff for scheduling these observations.

Matthew Bailes (Swinburne University of Technology-OzGrav) on behalf of the
SUPERB and OzGrav collaborations.

We report on further Fast Radio Burst (FRB) search observations of GW counterpart
SSS17a/DLTck (eg. Coulter et al., LVC GCN 21529
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 ) with the Parkes 64m Radio
Telescope in FRB search mode.

Three additional hours of data were retrieved and reduced from 0.38-0.5d after the
GW event using the same observing setup as that used in GCN circular 28199
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 .
The observations commenced at UTC 2017-08-18 06:49:31 (2h) and
UTC 2017-08-18 08:50:36 (1h). No FRBs were detected with a flux limit
of 1.4 Jy (w/64 us)^{-1/2} where w is the observed width of the FRB in
microseconds.

D. Kaplan (UWM), I. Brown (UWM), M. Sokolowski (Curtin University), R. Wayth (Curtin University), T. Murphy (University of Sydney), D. Dobie (University of Sydney), C. Lynch (University of Sydney), and K. Bannister (CSIRO) on behalf of the MWA collaboration.

We have observed a 20 x 20 deg field-of-view centered on the  LIGO/Virgo G298048 localization region  (LVC GCN #21513
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 ) with the Murchison Widefield Array.  We observed 2017-08-18 07:07 UT to 2017-08-18 09:35 UT at a central frequency of 185 MHz and with a bandwidth of 30 MHz.  No emission was detected at the position of NGC 4993.  The RMS noise was 17 mJy/beam (note that the array is in the process of being reconfigured, so only 5/16 of the tiles are operational).   Analysis of subsequent epochs with the reconfigured array is underway.

We thank the MWA Operations team for supporting these observations.

M. Kramer, A. Kraus, R. Eatough (MPI fuer Radioastronomie)

The 100-m Effelsberg telescope of the MPIfR  observed the location of SSS17a 
(Coulter et al. 2017, LVC GCN 21529
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 ) using the position provided by Adams et al.
(LVC GCN 21816
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 ). Observations were conducted at 5, 15 and 32 GHz; none of them
detected a counterpart.

Observations at 32 GHz were performed at 10/9/2017 at UT 13:35 with the 100m telescope under moderate weather 
conditions using its secondary focus 9mm multi-beam receiver. In total, six maps were performed
on the position of SSS17a. Data analysis was done with the MPIfR���s software packages 
���Toolbox��� and ���Nod3��� (see M��ller et al., 2017). First, some weather effects were removed by 
subtracting the maps of one of the ���Off���-Horns from the ���On���-Horn. After some additional
baseline adjustment, the data was averaged and calibrated in Jy. Calibration parameters 
were determined by a similar observation of 3C286. The rms of the final map was 30 mJy 
(due to imperfect weather conditions and low elevation). Efforts are ongoing to
improve those limits.

Observations at C-band were also conducted at 10/9/2017 13:10 UT.  No source was detected and limits do not
improve on previous reports (e.g. Paragi et al., LVC CGN 21763; Alexander et al., LVC CGN 21851).

At a central frequency of 14.6 GHz, we used a cryogenically cooled
receiver (summed polarisations for 128 spectral channels, across a
bandwidth of 500 MHz, and with a data sampling interval of ��� 65 us) on
15/9/2017 (MJD 58011.537210648) for approximately 4025 seconds. Data
have been dedispersed in the range 0 to 50 000 pc cm���3 and analysed
for periodic signals and transient burst like events (e.g. FRBs) using
single pulse search tools in the presto software package
(http://www.cv.nrao.edu/ sransom/presto/).

For a 10-sigma detection threshold, we achieve the following limits to
periodic signals: 76 uJy and 52 uJy for duty cycles of 10% and 5%,
respectively. Note that at this frequency, weather effects can
decrease the sensitivity by at least a factor of two. More accurate
flux calibration using a noise diode and reference source is on-going.

At this observing frequency our transient search has revealed signals
that cannot yet be easily distinguished from terrrestrial radio
interference. Sensitivity limits for transients depend upon the
unknown intrinsic pulse width and pulse broadening factors, however
for a single pulse of width 1,3,5 and 10 ms, and DM of 1000 pc cm���3
(smearing at the central frequecny channel = 10.414 us), we find
6-sigma flux density limits of 0.32, 0.19, 0.15 and 0.10 Jy
respectively.

Giambattista Aresu, Matteo Bachetti, Franco Buffa, Marta Burgay, Marco 
Buttu, Teresa Caria, Ettore Carretti, Paola Castangia, Giuseppe Carboni, 
Silvia Casu, Raimondo Concu, Alessandro Corongiu, Gianluigi Deiana, 
Elise Egron, Antonietta Fara, Francesco Gaudiomonte, Vincenzo Gusai, 
Adelaide Ladu, Sara Loru, Silvia Leurini, Lino Marongiu, Andrea Melis, 
Pino Melis, Carlo Migoni, Sabrina Milia, Alessandro Navarrini, Andrea 
Orlati, Pierluigi Ortu, Stefano Palmas, Alberto Pellizzoni, Delphine 
Perrodin, Maura Pilia, Tonino Pisanu, Sergio Poppi, Andrea Possenti, 
Andrea Saba, Giampaolo Serra, Mauro Serrau, Gabriele Surcis, Alessio 
Trois, Valentina Vacca, Gian Paolo Vargiu - all from INAF Osservatorio 
Astronomico di Cagliari
Viviana Casasola - INAF Osservatorio Astrofisico di Arcetri
Giancarlo Ghirlanda - INAF Osservatorio Astronomico di Brera
Simona Righini, Matteo Stagni - INAF Istituto di Radioastronomia di Bologna
on behalf of GRAvitational Wave Inaf TeAm (GRAWITA) report:.

Following the VLA detection of a radio source (Mooley et al., LVC GCN 
21814
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 ; Corsi et al., LVC GCN 21815
Loading...
 
 ) coincident with the optical 
transient SSS17a/DLT17ck (Coulter et al. LVC GCN 21529
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 ; Allam et al., 
LVC GCN 21530
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 ; Yang et al., LVC GCN 21531
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 ), the possible counterpart of 
G298048 (LVC, LVC GCN 21505
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 ) in NGC 4993, we carried out observations of 
the field with the Sardinia Radio Telescope at 7.2 GHz (central 
frequency, with a bandwidth of 680 MHz). Observations were conducted on 
the days 2017-09-07, 2017-09-08, 2017-09-09, and 2017-09-19, for a total 
of approximately 18 hours of on-the-fly mapping over the entire 
region and about 8 minutes of on-source time. The target was observed at 
low elevations (<27 degrees) and the weather conditions were suboptimal 
for a large fraction of the observing time.

Data were taken to image a field of 0.3x0.3 deg^2 centred on the position
of the source that was reported to be detected with the VLA on 2017-09-03.
Calibration and analysis were conducted following two different
approaches:

- according to the procedures described in Egron et al. (2017,MNRAS, 470, 1329), we did
not detect any source and find an upper limit for a steady source at the
position of the target of 1.5 mJy (1 sigma) and a global rms of the image
of 0.9 mJy/beam (1 sigma);

- by using the map-making software described in Carretti et al. (2010, MNRAS, 405, 1670), 
 we did not detect any source at that position, at an upper limit of
0.5 mJy rms (1 sigma) as computed for a steady source.

According to the condition of each single observation, we find an upper
limit ranging between at most 1 and 3 mJy for each observing session. At
present a refinement of the analysis is ongoing and observations at
subsequent epochs and at higher frequencies are planned.

-- 
Enzo Brocato
INAF - Osservatorio Astronomico di Roma
Via di Frascati 33,  
I-00040 Monteporzio Catone, Italy
Phone:  +39 0694286438 Fax: +39 06 9447243
skype: enzo.brocato
URL: SpoT Group Homepage: www.oa-teramo.inaf.it/SPoT

C. McCully, D. A. Howell, G. Hosseinzadeh, D. Hiramatsu, I. Arcavi, S.
Vasylyev (UCSB/Las Cumbres Obs), S. Valenti (UC Davis)

and

L. P. Singer (NASA/GSFC), C. Fremling (Caltech), and M. M. Kasliwal
(Caltech) on behalf of the GROWTH (Global Relay of Observatories
Watching Transients Happen) collaboration report:

We observed the optical transient, SSS17a/DLT17ck (Coulter et al., LVC GCN
21529
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 ) on 2017-08-19 08:36:22, +1.83 days after the LIGO/Virgo trigger
G298048 (LVC GCN Circ. 21509
Loading...
 
 , 21513
Loading...
 
 ), for one hour with the robotic FLOYDS
instrument mounted on the Las Cumbres Observatory Faulkes Telescope South
at the Siding Spring Observatory in Australia. We detect the continuum of
the transient at low signal-to-noise level.

We also observed SSS17a/DLT17ck on 2017-08-20 01:01:54, +2.51 days after
the LIGO/Virgo trigger, with the Gemini Multi-Object Spectrograph (GMOS) on
the Gemini-South 8-m telescope. We observed in our red setting for 763
seconds and 128 seconds in our blue setting until the telescope reached its
altitude limit. We again detect the continuum at low signal to noise level
due to the high airmass at which the observations were made and the limited
exposure times due to observing constraints.

We thank the LCO staff, specifically Mark Bowman and Mark Willis, and the
Gemini staff, specifically Karleyne Silva and Laura Ferrarese, for their
assistance with these observations.

R. Ricci (INAF), M. Wieringa (CSIRO), L. Piro (INAF)
and E. Troja (UMD/GSFC) report:

On 15 Sep 2017, 3rd epoch of our monitoring campaign, we observed
the field of SSS17a (Coulter et al.,LVC GCN 21529
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 ) with the Australia
Telescope Compact Array (ATCA) at the central frequencies of 16.7 and
21.2 GHz, each with a bandwidth of 2 GHz.

At the position of the optical/IR source (Adams et al., LVC GCN 21816
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 )
we report the following 3-sigma upper limit:

17/21 GHz flux density < 42 uJy

We thank the CSIRO staff for approving and executing the observations.

Matthew Bailes (Swinburne University of Technology-OzGrav) on behalf of
SUPERB and OzGrav collaborations.


We report on Fast Radio Burst (FRB) search observations of GW counterpart
SSS17a/DLTck (eg. Coulter et al., LVC GCN 21529
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 ) with the Parkes 64m Radio
Telescope in FRB search mode.

Two 1-hour observations were searched for FRBs with Dispersion Measures
(DMs) ranging from 0 to 2000 pc/cc 2.5 days after the GW event.  The start
UT of the 1hr integrations was 2017-08-20 01:44:32 and 2017-08-20 02:50:14.
No FRBs were detected with a flux limit of 1.4 Jy (w/64 us)^{-1/2} where w
is the width of the FRB in microseconds.  An FRB in the host galaxy might be
expected to have a DM of ~55 pc/cc plus the unknown contribution from any
remnant.  FRBs of luminosity similar to those observed from the repeating
FRB 121102 would be detected at the distance of NGC 4993 with very high
significance (SNR>>100).

A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), 
A. Moskvitin (SAO RAS), M. Krugov (AFIF) report on behalf of IKI-GW 
follow-up collaboration:

We report a photometry  of  the counterpart SSS17a/DLT17ck (Coulter et 
al. GCN 21529
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 ;  Yang et al., GCN 21531
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 ) of LIGO/Virgo trigger G298048 
(LIGO Scientific Collaboration and Virgo Collaboration, GCNs 21509
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 , 
21513
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 )  with RC-1000 1m telescope of CHILESCOPE observatory (GCNs 21618
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 , 
21635
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 , 21644
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 ). The observations carried out in a clear filter in four 
epochs. We used last epoch (7.49278 days after trigger)  to construct a 
mask for subsequent mask subtraction. The PSF photometry is based on 
several nearby USNO-B1.0 stars (R2 magnitudes).

Photometry of the transient SSS17a/DLT17ck is following


Date       UT start   t-T0    Filter Exp.    OT     Err.
                       (mid, days)     (s)

2017-08-19 23:30:33  2.46157  CR     10*180  19.12  0.06
2017-08-20 23:21:09  3.47840  CR     13*180  20.04  0.08
2017-08-21 23:32:09  4.49409  CR     22*180  20.14  0.12
2017-08-24 23:53:39  7.49278  CR     20*180 >21.0 (3 sigma upper limit)

A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni
(Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav),
D. Dobie (University of Sydney), D. Kaplan (UWM), C. Lynch (University of
Sydney), T. Murphy (University of Sydney), on behalf of a joint effort
between OzGrav and the VAST collaboration.


We have further analysed the Very Long Baseline Array (VLBA) observations of
the field containing NGC 4993 and SSS17a/DLT17ck (Deller et al., LVC GCN
21588
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 ; Deller et al., LVC GCN 21850
Loading...
 
 ), producing images centered on the
sub-mJy radio source at the centre of NGC 4993 (Alexander et al., LVC GCN
21545
Loading...
 
 ;  Alexander et al., LVC GCN 21548
Loading...
 
 ; Bannister et al., LVC GCN 21559
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 ;
Alexander et al., LVC GCN 21589
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 ; Corsi et al., LVC GCN 21614
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 ).

The source is detected with a flux density of 0.22 mJy (9 sigma
significance, flux calibration scale uncertainty estimated at 20%).  The
data is consistent with either an unresolved or marginally resolved source,
while comparison with the flux densities estimated by the ATCA and VLA
observations indicate that most (or possibly all) of the source flux is
contained within this milliarcsecond-scale component. Taking the synthesized
beam size of 2.5 x 1.0 mas as an upper limit to the source size, the
inferred lower limit for the brightness temperature is 1.6 x 10^6 K,
consistent with an AGN interpretation.  The position obtained is
13:09:47.69398 -23:23:02.3195 (J2000), with estimated uncertainties
(dominated by systematics) of <=1 mas in each coordinate.

M. Diaz, L. Macri, J.L. Nilo Castellon, B. Sanchez, C. Mendes, C. Colazo, M. Schneitter, C. Girardini, D. Garcia Lambas, M. Beroiz, A. Zadrozny, R. Camuccio, M. Castillo. J. Garcia for the TOROS collaboration

We have completed the PSF photometry of the observations of GW170817 carried out at the T80S telescope and the EABA telescope on 08/18/2017 and 08/19/2017 (GCN 21619
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 , GCN, 21620). We calibrated our measurements using the Pan-STARRS1 catalog available at STScI, using their reported PSF magnitudes and uncertainties. The mid-point of our observations was 1.467d after the GW trigger - LIGO/Virgo G298048- (Julian Date of 2457984.495). At that time, we measured magnitudes of g=18.60, r=17.99, i=17.80 with uncertainties of +-0.02 mag.
Additionally with our observations utilizing the EABA telescope we obtained  r=18.78+-0.03 at 2.456d after the GW trigger -LIGO/Virgo G298048-. 


_______________________________________
Mario C. D��az
Director
Center for Gravitational Wave Astronomy and
Professor
Department of Physics and Astronomy
The University of Texas Rio Grande Valley
(956) 882-6690   FAX: (956) 882-6726
mario.diaz@utrgv.edu    http://www.mariodiaz.org/
______________________________________
No ceder Carhue al huinca. Calfucura (1873)

P. J. Hancock, S. J. Tingay, J. S. de Gois, T. Booler (ICRAR, Curtin University), H. A. R. Devillepoix, P. A. Bland, M. C. Towner, E. K. Sansom, R. M. Howie (DFN, Curtin University), D. L. Kaplan (UWM)

The Desert Fireball Network (DFN) is a network of 50 remote cameras located in the Western and South Australian desert designed for the detection and triangulation of Fireballs and bright meteors. The DFN cameras consist of a Nikon D800E camera equipped with a Samyang 8mm f/3.5 UMC Fish-eye CS II lens. The cameras capture full sky images with a cadence of 30s from sunset to sunrise every night of the year.

We retrieved images from a camera located at Wooleen Station (27.0872 deg S, 116.1611 deg E).  We analysed the images from the 17th of August from 12:39:28-12:49:28 UT: 2 minutes before the GW trigger to 7 minutes after. At this time the host galaxy NGC 4993 was at 20 degrees elevation, reducing the image sensitivity from 6th to 4th magnitude. The images show no persistent or transient sources in a 3 degree radius of NGC 4993, to a limiting visual magnitude of +4.

S. Goedhart (SKA South Africa) reports on behalf of a larger team:

MeerKAT, currently being commissioned, observed the location of SSS17a 
(Coulter et al. 2017, LVC GCN 21529
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 ) in L band between 2017-08-25 and 
2017-09-06. Preliminary analysis of the observation from 2017-09-06 does 
not reveal a radio afterglow, with a 3-sigma upper limit of 75 uJy at 
1.5 GHz. Further observations and analysis are planned.

We thank the SKA South Africa team for enabling these observations.

���Z. Cano (IAA-CSIC), U. G. Jorgensen (Univ. of Copenhagen), G. Hodosan
(IAA-CSIC, Univ. of St Andrews), R. Figuera Jaimes (Univ. of St Andrews),
Y. I. Fujii (Univ. of Copenhagen; Nagoya Univ.), and M. Rabus (Pontificia
Univ. Catolica de Chile, MPIA)

We report on observations obtained with the 1.54-m Danish Telescope located
at La Silla, Chile, of the GW counterpart SSS17a/DLT17ck (Coulter et al.,
LVC GCN 21529
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 ). Observations were obtained on 2017, August 19th, 21st and
22nd in the I-band (all three dates), and z-band (19th only). A summary of
the observations follows:

Date        UT Start    Exposure time (s)    Filter
----------------------------------------------------------------------
19-August    23:41:45.6    6 x 150            I
19-August    23:44:49.9    6 x 150            z
21-August    23:17:51.8    25 x 100        I
22-August    23:23:57.3    40 x 100        I

Image subtraction of the co-added I-band images obtained during the first
two nights reveals a residual transient at the following position:

RA, Dec (J2000): 13:09:48.11 -23:22:53.0

With an estimated uncertainty of ~0.5''. This position is consistent with
that found by other groups within its uncertainty radius.

Further analysis of the images is currently underway, including the precise
photometric calibration of the optical transient.���

J. Tonry (IfA), K. W. Smith (QUB), L. Denneau, A. Heinze, B. Stalder,
H. Weiland (IfA), C. W. Stubbs (Harvard), S. J. Smartt (QUB), A. Rest
(STScI), K. C. Chambers (IfA), T.-W. Chen (MPE), M. Coughlin
(Harvard), D. R. Young, (QUB), M. E. Huber (IfA), D. E. Wright (QUB),
H. Flewelling, T. Lowe, E. A. Magnier, A. S. B. Schultz, C. Waters, R.
J. Wainscoat, M. Willman (IfA)


During its normal survey mode, the ATLAS survey project (Tonry et al.
2011, Stalder et al. 2017) frequently observed the field containing
galaxy NGC4993 during the period between 57380.64463 and 57966.26370
(602 to 16 days before G298048; the LIGO Scientific Collaboration and
the Virgo Collaboration GCN 21509
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 ) and the first discoveries and
detections of the optical/NIR transient SSSa17a/DLT17ck (Coulter et
al. GCN 21529
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 , Allam et al. GCN 21530
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 ,Valenti et al. GCN21531
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 ,
Melandri et al. 21532).

We have completed a search for variability or eruptions at the
position of the optical transient in the 414 images over this period.
These images were taken typically with 4-5 images per night (30 second
exposures).

ATLAS observes in two wide-band filters, called "cyan" or "c:, which
roughly covers the SDSS/Pan-STARRS g and r filters, and ���orange��� or
"o", which roughly covers the SDSS/Pan-STARRS r and i. The position
was observed 414 times in one or other filter and on each of these we
forced flux measurements at the astrometric position of the transient
on the difference image. We used the Pan-STARRS images for the
astrometric postion of SSS17a/DLT17ck (Chambers et al. GCN 21553
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 )

We measured 5-sigma flux limits and any epochs with greater than
5-sigma detections. The 5-sigma flux limits were in the range 18.5 +/-
0.4 (AB mag, median and standard deviation) and (19.4 +/- 0.4). We
found 44 images which formally had flux detections greater than
5-sigma, but on visual inspection we rule out these being real flux
variability at the transient position. They all appear to be residuals
from the host galaxy subtraction. With ATLAS, we rule out any
variability down to 18.5 to 19.4 (filter dependent) during a period
601 to 16 days before discovery of the optical transient. The last
image was on 57966.26370 (2017-08-01 06:19) with a 5-sigma limit of 
o < 18.2.

Lei Hu (Purple Mountain Observatory), Lifan Wang (Texas A&M University/Purple Mountain Observatory), Tianrui Sun (Purple Mountain Observatory), Ma Bin (National Astronomical Observatory of China), Xiaofeng Wang (Tsinghua University), Xuefeng Wu (Purple Mountain Observatory), and the AST3 team
and
Jeff Cooke (Swinburne/OzGrav), Igor Andreoni (Swinburne/OzGrav/AAO) on behalf of OzGrav

We report observations of the GW counterpart SSS17a/DLT17ck (e.g., Coulter et al., LVC GCN 21529
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 ; Allam et al., LVC GCN 21530
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 ; Yang et al., LVC GCN 21531
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 ) with the second of Antarctica Schmidt Telescopes (AST3-2).  AST3-2 is a 50cm optical telescope located at Kunlun Station at Dome A in the Antarctic.  

Observations were carried out from August 18 through August 28 in g-band filter.  Data transfer from Antarctica has recently completed.  A source with g-band magnitude 18.15 +/-0.1 was detected on  2017-08-18T14:42.6796 (mean value) at the position of SSS17a/DLT17ck.  Note the signal was identified from a coadded image and the observational information about the component images are as follows.

Image-ID    UT datetime of start of observation     Exposure time
0818-48         '2017-08-18T13:58:11.6138'                  300.00
0818-49         '2017-08-18T14:03:14.8497'                  300.00
0818-50         '2017-08-18T14:09:07.4807'                  300.00
0818-51         '2017-08-18T14:14:10.7166'                  300.00
0818-52         '2017-08-18T14:28:36.9730'                  300.00

All observation from AST3-2 are reported below.  All time mentioned is UT time of start of exposure:

August 18 
The observation is not regular, so we list them in details

Group1: observation started from [ID 48]2017-08-18T13:58:11.6138 to [ID 51]2017-08-18T14:14:10.7166
Total 4 images with constant exposure time 300s and regular cadence about 54s
Group2: observation started from [ID 52]2017-08-18T14:28:36.9730 to [ID 72]2017-08-18T17:57:39.5806
Total 21 images with constant exposure time 300s and regular cadence about 54s

August 20 
observation started from [ID 15]2017-08-20T12:51:40.934 to [ID 74]2017-08-20T18:43:29.7538 
Total 60 images with constant exposure time 300s and regular cadence about 54s

August 21 
observation started from [ID 6]2017-08-21T13:10:22.4063 to [ID 55]2017-08-21T17:58:16.8969 
Total 50 images with constant exposure time 300s and regular cadence about 54s

August 23 
observation started from [ID 692]2017-08-23T13:13:02.8477 to [ID 722]2017-08-23T16:10:14.0793
Total 31 images with constant exposure time 300s and regular cadence about 54s

August 24
observation started from [ID 871]2017-08-24T15:52:00.3374 to [ID 917]2017-08-24T20:36:43.9922
Total 47 images with constant exposure time 300s and regular cadence about 54s

August 25
observation started from [ID 1153]2017-08-25T14:07:25.7058 to [ID 1168]2017-08-25T15:36:08.5704
Total 16 images with constant exposure time 300s and regular cadence about 54s

August 27
observation started from [ID 1204]2017-08-27T13:50:45.9777 to [ID 1223]2017-08-27T15:43:31.4251
Total 20 images with constant exposure time 300s and regular cadence about 54s

August 28
observation started from [ID 731]2017-08-28T15:12:09.9744 to [ID 738]2017-08-28T15:52:53.1212
Total 8 images with constant exposure time 300s and regular cadence about 54s

Processing of the AST3-2 images is in progress.

M. Wieringa (CSIRO), R. Ricci (INAF), L. Piro (INAF) and
E. Troja (UMD/GSFC) report:

On 08 Sep 2017, we observed the field of SSS17a (Coulter et al.,
LVC GCN 21529
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 ) with the Australia Telescope Compact Array (ATCA)
at the central frequencies of 16.7 and 21.2 GHz, each
with a bandwidth of 2 GHz.

At the position of GW counterpart (Adams et al.,
LVC GCN 21816
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 ) we report the following 3-sigma upper limit:

17/21 GHz < 35 uJy

Further observations are planned.

We thank the CSIRO staff for approving and executing these observations.

K. D. Alexander, E. Berger, T. Eftekhari, W. Fong, and R. Margutti report
on behalf of a larger collaboration:

We observed the location of the optical counterpart of LIGO/Virgo
G298048 (Coulter
et al. LVC GCN 21529
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 ; Allam et al. LVC GCN 21530
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 ) with the Very Large Array
at a frequency of 6 GHz (C-band) on September 5.925 UT.  We do not detect
any significant radio emission (S/N>3) and therefore cannot confirm the
radio detection reported two days earlier by Corsi et al. (LVC GCN
21815
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 ) for a comparable integration time on source and at the same
frequency.  This indicates either rapid fading (not expected for off-axis
jet emission), significant variability (not expected from scintillation
given the small source distance and hence large angular size), or a
spurious detection in the previously reported observations.   Further
observations are underway.

A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni (Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav), D. Dobie (University of Sydney), D. Kaplan (UWM), C. Lynch (University of Sydney), T. Murphy (University of Sydney), on behalf of a joint effort between OzGrav and the VAST collaboration.


Radio observations with the Very Long Baseline Array from 2.5 weeks ago (Deller et al., LVC GCN 21588
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 ) covering the field surrounding the optical transient SSS17a/DLT17ck (e.g., Coulter et al., LVC GCN 21529
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 ; Allam et al., LVC GCN 21530
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 ; Yang et al., LVC GCN 21531
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 ) have now been correlated and analysed.  

Each observation spanned 6.5 hours, with 256 MHz of bandwidth (dual polarisation) centered on 8.7 GHz, giving an image rms of approximately 22 microJy.  A 12500x12500 pixel image (2.5 x 2.5") image was produced, centered on SSS17a/DLT17ck.  As expected given non-detections with the VLA (Alexander at al., LVC GCN  21589
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 ; Corsi et al.,  LVC GCN 21613
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 ; Corsi et al., LVC GCN 21614
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 ; Corsi et al., LVC GCN  21636
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 ) and ATCA (Bannister at al., LVC GCN 21559
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 ; Kaplan et al., LVC GCN 21574
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 ; Lynch et al.,  LVC GCN 21670
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 ) close in time to these VLBA observations, we do not detect any radio emission, and place 5.5 sigma upper limits as follows:

Observation center MJD 57985.9: 5.5 sigma upper limit 125 microJy.
Observation center MJD 57986.9: 5.5 sigma upper limit 120 microJy.

Combining these two observations places a deeper limit, with image rms 16 microJy: 5.5 sigma upper limit 88 microJy.

We thank the staff of the Long Baseline Observatory for supporting these observations.

T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech),
M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U
Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J.
Tsai (Virginia Tech), C. Yancey (U Maryland)
 
We report the preliminary detection of a radio source in a beam centered
on RA 13.096h, Dec -22.024deg, the LIGO/Virgo G298048 event coordinates,
during a four-hour observation on August 17 (19:15 UTC, 6.6 hours after
the GW trigger), using station 1 of the Long Wavelength Array (LWA1)
[GCN 21680]. Simultaneous ON-OFF observations were taken at 25 MHz and
45 MHz, and follow-up observations were taken August 24 (19:50 UTC), one
week after the initial observations. Comparison of the ON-OFF
observations for the two epochs indicate the apparent presence of a ~20
Jy source, at 25 MHz, in the beam on RA 13.096h, Dec -22.024deg. There
is no difference between the ON-OFF results at 45 MHz, for the two
epochs. Further analysis and follow up observations are underway.

T. Murphy (University of Sydney), E. Lenc (University of Sydney),
C. Lynch (University of Sydney), D. Dobie (University of Sydney),
D. Kaplan (UWM), K. Bannister (CSIRO), on behalf of the VAST collaboration.

Following the reported VLA detection of a radio source (Mooley et al.;
LVC GCN 21814
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 , Corsi et al.; LVC GCN 21815
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 ) coincident with the optical
transient SSS17a (Coulter et al. LVC GCN 21529
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 ) we conducted further
observations of NGC 4993 with the Australia Telescope Compact Array at
5.5 and 9 GHz. Observations started at 2017-09-04 22:43:04 UT and ended
at 2017-09-05 10:03:04 UT with approximately 9.5 hours of on-source time.

We did not make a robust detection, although there is marginal emission
at the 4-sigma level, at a position consistent with that reported by
Mooley at al. and Corsi et al. This could be associated with the host
galaxy or the optical transient.

Analysis is ongoing, and subsequent epochs are planned.

Thank you to CSIRO staff for supporting these observations.

A. Grado (INAF-OAC), F. Getman (INAF-OAC), L. Limatola (INAF-OAC),
E. Cappellaro (INAF-OAPD), M. Branchesi (GSSI), S. Covino (INAF-OAB), P.
D'Avanzo (INAF-OAB),  A. Melandri (INAF-OAB), L. Amati (INAF-IASF Bo), L.
A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD),
M.T. Botticella (INAF-OAC),  S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC),
D. Fugazza, M. Lisi (INAF-OAR), G. Greco
(Urbino University/INFN Firenze), L. Nicastro (INAF-IASF Bo),
E. Palazzi (INAF, IAFS Bo), E. Pian (INAF, IAFS Bo), S. Piranomonte
(INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani
(INAF-OAC), G. Stratta (Urbino University/INFN Firenze),
G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella
(INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of
GRavitational Wave Inaf TeAm report:


Observations of 1 square degrees of the skymap of the Advanced LIGO
and Virgo trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) were performed with
the VLT Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal
equipped with OMEGACAM. The observations are centered on the galaxy
NGC4993.  The images were taken in the i_SDSS filter with a total exposure
of 1200s. The observations started at 2017-08-31T 23:22:12.442 UTC and
finished at 2017-08-31T 23:39:26.585. The Optical Transient (OT) is not
visibile in the coadded image. The completeness at 50% for point-like
sources is 22.53 AB mag.  Automatic data reduction with the VSTTube
pipeline (Grado et al. 2012 Mem.SAIt 19, 362 ) was completed.
We acknowledge excellent support from the ESO User Support Department and
from ESO observing staff in Paranal.

S. M. Adams, M. M. Kasliwal, N. Blagorodnova (Caltech)

report on behalf of a larger GROWTH (Global Relay of Observatories Watching
Transients Happen) collaboration

We registered our HST F336W image (PI Kasliwal) with the Gaia astrometric
catalog to derive a more precise position of SSS17a (Coulter et al. LVC GCN
21529
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 ). We find a position of 13:09:48.071 -23:22:53.37 with astrometric
residuals of 0.05". This new position is consistent with the position of
the radio source reported in companion GCNs by Corsi et al. LVC GCN 21815
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and Mooley et al. LVC GCN 21814
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 .

A. Corsi (TTU), G. Hallinan (Caltech), K. Mooley (Hintze Fellow, Oxford), D.A. Frail (NRAO), M.M. Kasliwal (Caltech),  
N.T. Palliyaguru (TTU) report on behalf of a larger GROWTH collaboration:

We observed the field of SSS17a/DLT17ck (e.g., Coulter et al. LVC GCN 21529
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 ; Allam et al. LVC GCN 21530
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 ; 
Yang et al. LVC GCN 21531
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 ), the possible counterpart of G298048 (LVC, LVC GCN 21505
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 ) in NGC 4993, with 
the Karl G. Jansky VLA in its B configuration (program 16A-206; PI: Corsi). The observation lasted about 
1.25 hr, starting on 17-Sep-03 23:30:57 UT, and was conducted in C-band (approximate central frequency of 
6 GHz). We report the detection of a radio source with S/N of about 5. This source was not seen in previous 
epochs down to similar limits (e.g. Corsi et al., LVC GCN 21664
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 ). The radio position is within the astrometric 
errors of the optical position of SSS17a. We have confirmed this source through comparison with contemporaneous 
S-band observations reported by Mooley et al. (see companion LVC GCN by Mooley et al.). Further observations 
are planned immediately.

We thank the VLA staff for scheduling these observations.

K. P. Mooley (Hintze Fellow, Oxford), G. Hallinan (Caltech) and A. Corsi
(TTU) report on behalf of the JAGWAR and GROWTH teams

We observed the location of SSS17a in S band (2-4 GHz) as part of the
Jansky Array mapping of GW bursts as Afterglows in Radio (JAGWAR)
program on 01-02 Sep 2017 for 5 hours. We report the detection of a
source with a signal-to-noise ratio of ~5, consistent within the
astrometric uncertainty of the optical transient (Coulter et al. 2017,
LVC GCN 21529
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 ). We have confirmed this source through comparison with
contemporaneous C band observations reported by Corsi et al. (see
companion LVC GCN). Multifrequency monitoring of this source with the
VLA and other radio facilities has been initiated.

We thank the VLA staff for scheduling these observations.

Javier Moldon and Rob Beswick (JBO-Manchester University) for the EuroVLBI team


We monitored the field around the optical counterpart SSS17a (Coulter
et al., LVC 21529) with the e-MERLIN radio interferometer between
August 23 and 28, 2017. We conducted observations at C band centred at
5 GHz with a bandwidth of 512 MHz for 5 hours between 13:00 and 18:00
UTC in each consecutive day.

No significant detection above 5-sigma level is found in the runs with
individual rms noise levels between 31 and 39 microJy/beam. The upper
limits at 5-sigma level are 180, 160, 160, 190, 150, 150 microJy/beam
for days 23 to 28 August, respectively. The average half power beam
width of the images is 266 mas x 33 mas with a position angle of 0
degrees. An image produced combining the data from the six runs yields
an upper limit of 70 microJy/beam at the 5-sigma level.

Additional observations are planned with e-MERLIN to continue the
monitoring of the transient source.

e-MERLIN is a National Facility operated by the University of
Manchester at Jodrell Bank Observatory on behalf of STFC.



-- 
Zsolt Paragi
Head of User Support

Joint Institute for VLBI ERIC (JIVE)    Web:  http://www.jive.eu
Oude Hoogeveensedijk 4                  Phone:  +31 (0)521-596-536
7991 PD  Dwingeloo                        Mobile:  +31 (0)629-034-718
the Netherlands                                Fax:  +31 (0)521-596-539

E. Troja (UMD/GSFC), R. Ricci (INAF), M. Wieringa (CSIRO),
and L. Piro (INAF) report:

On 01 Sep 2017, we observed the field of SSS17a (Coulter et al.,
LVC GCN 21529
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 ) with the Australia Telescope Compact Array (ATCA)
at the central frequencies of 16.7, 21.2, 43 and 45 GHz, each
with a bandwidth of 2 GHz.

At the position of the optical/IR and X-ray source (Troja et al.,
LVC GCN 21765
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 , 21787
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 ) we report the following 3-sigma upper limits:

17/21 GHz���������� < 50 uJy
43/45 GHz���������� < 90 uJy

Further observations are planned.

We thank the CSIRO staff for approving and executing these observations.

D. Haggard, M. Nynka (McGill), V. Kalogera (Northwestern), Phil Evans (Leicester), and Brad Cenko (NASA/GSFC)

We report a new ~47 ks Chandra X-ray observation (ObsID 18988, PI Haggard) of the LVC trigger G298048, a.k.a. GW170817, beginning 2017 September 02, approximately 16 days after the trigger. These observations include the optical transient SSS17a (Coulter et al., LVC GCN 21529
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 ) and the Swift area of interest (Evans et al., LVC GCN 21612
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 ).

We detect X-ray emission from two point sources and from one extended source: (i) point-source X-ray emission at the location of the optical transient SSS17a (Coulter et al., LVC GCN 21529
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 ; Troja et al., LVC GCN 21765
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 ; Margutti LVC GCN 21786
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 ; Troja et al., LVC GCN 21787
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 ), (ii) another point source at the location of the Swift X-ray emission (Evans et al., LVC GCN 21612
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 ) also reported by Margutti et al. (LVC GCN 21786
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 ), and (iii) extended emission from the host galaxy NGC 4993 (Evans et al., LVC GCN 21612
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 ; Margutti et al., LVC GCN 21648
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 ).

We analyze these new data in combination with DDT Chandra observations acquired one day earlier (ObsID 20728, PI Troja) and report tentative evidence for decreasing fluxes from both X-ray point sources (1-sigma errors are ~1E-15 erg/s/cm2):

X-ray Counterpart to Optical Transient SSS17a (assuming PL w/ gamma=2.4):

Sep 01: 5.1E-15 erg/s/cm2 (0.3-8 keV)
Sep 02: 4.5E-15 erg/s/cm2 (0.3-8 keV)

Chandra X-ray Point Source (assuming PL w/ gamma=2.0):

Sep 01: 3.5E-15 erg/s/cm2 (0.3-8 keV)
Sep 02: 2.7E-15 erg/s/cm2 (0.3-8 keV)

We thank Belinda Wilkes and the entire Chandra team for their support of these observations.

E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), T. Sakamoto (AGU),
S. B. Cenko (NASA/GSFC), and A. Lien (UMBC/GSFC) report on behalf
of a larger collaboration:

We re-observed the field of SSS17a (Coulter et al., LVC GCN 21529
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 ) with
the Chandra X-ray Observatory (PI: E. Troja) on 2017-09-01
(~15 days after the LVC trigger) for a total exposure of 47 ks.

The X-ray source reported in Troja et al. (LVC GCN 21765
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 ) is still
detected.
At the position of the optical/IR transient we measure ~17 net counts.
By describing the spectrum with an absorbed power-law we estimate a flux
of approximately 4.5E-15 erg/cm2/s (0.5-8.0 keV).

We thank Belinda Wilkes and the entire Chandra team for approving and
scheduling these observations.

W. Fong, R. Margutti (Northwestern), D. Haggard (McGill) report on behalf
of a larger collaboration:


We analyzed observations of the field of the EM counterpart to LVC trigger
G298048 with the Chandra X-ray Observatory (CXO; ObsID 20728, PI Troja)
starting on 2017 Sep 1.640 UT (15.1 days after the LVC trigger time). In 50
ksec of observations, we clearly detect X-ray emission at the location of
the optical transient (Coulter et al., LVC GCN 21529
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 ; Allam et al., LVC GCN
21530
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 ; Sheng Yang et al., LVC GCN 21531
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 ; Chambers et al., LVC GCN 21553
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 ),
suggesting continued X-ray emission from the transient (Troja et al., LVC
GCN 21765
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 ). Extended emission from the host galaxy (Margutti et al., LVC
GCN 21648
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 ; Evans et al., LVC GCN 21612
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 ) is still detected. We also note the
presence of a third X-ray source in the Swift/XRT error circle (Evans et
al., LVC GCN 21612
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 ; RA,Dec = 13:09:48.014,-23:23:04.93), that has not been
previously reported.

We thank Belinda Wilkes and the entire Chandra team for their great support
with these observations.

[GCN OPS NOTE(03sep17): This circular (21786) completely replaces 21784
(whose text was the result of a copy-paste mistake).]

F. Verrecchia (SSDC and INAF/OAR), M. Cardillo (INAF/IAPS), A. Bulgarelli
(INAF/IASF-Bo), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), G. Piano
(INAF/IAPS),  M. Pilia (INAF/OA-Cagliari), I. Donnarumma (ASI), C. Pittori
(SSDC and INAF/OAR), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi,
G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and
INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo),
A. Trois (INAF/OA-Cagliari), M. Marisaldi (INAF/IASF-Bo and Bergen
University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE
Team:

We performed  a dedicated analysis of AGILE Gamma-Ray Imaging Detector
(GRID) data in response to the detection on 2017-08-26 by Chandra of an
X-ray transient (Troja et al., LVC GCN 21765
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 ). This source is coincident
with the optical/IR transient SSS17a (Coulter et al., LVC GCN 21529
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 ) possibly
associated with GW170817A.

GRID data analysis covering the SSS17a position was performed in the energy
range 50 MeV - 10 GeV with integration times from 1 to 3 days centered at T0+9
days. Preliminary values of 2-sigma upper limits (UL) are reported below:

3.0e-10 erg cm^-2 s^-1 for a 1-day integration time
(from 26 August 00:00 UT to 27 August 00:00 UT);

1.9e-10 erg cm^-2 s^-1 for a 2-day integration time (from 26 August 00:00
UT to 28 August 00:00 UT);

1.3e-10 erg cm^-2 s^-1 for a 3-day integration time (from 25 August 00:00
UT to 28 August 00:00 UT).

These measurements were obtained with AGILE observing a large portion of
the sky in spinning mode. Additional analysis of AGILE data is in progress.

A. Cwiek (NCBJ), A. F. Zarnecki (UW), A. Mankiewicz (CFT PAS), A. Zadrozny (UTRGV, NCBJ) on behalf of the Pi of the Sky


Pi of the Sky telescope surveyed area (RA: 220 - 22 deg, DEC: -10 - 70) that overlap, in parts, with initial bayesstar skymap for G298048. Observations were conducted from INTA, Huelva Spain during nights 17th up to 21th of August. Is it worth noting that this area was well observed from 10th up 16th August giving a strong reference background.


Data was searched for any type of transients connected with objects from GLADE catalogue. Data analysis showed that it is unlikely to have an slowly fading optical transient. However two possible fast fading optical transients are still under investigations along with several other subprimes.


Investigated possible optical transients with positions:

RA                  DEC

20.876109    33.322977
354.050166  14.997596


We have performed our observations using two cameras using only IR-cut filter. Each camera have 20 by 20 degree field of view. For each observed field (20 by 20 degrees), the telescope has made five 10 s exposures twice a night. Observations have limiting brightness between 11.5 - 12 mag.

A.J. Levan (Warwick), E. Troja (UMD/GSFC), N.R. Tanvir (Leicester),
O. Fox (STScI), J. Hjorth (DARK, Copenhagen), S. B. Cenko (GSFC),
A. S. Fruchter (STScI), R. Ryan (STScI), Z. Cano (Granada), A. de
Ugarte Postigo (Granada), P. Evans (Leicester), J. Greiner (MPE
Garching), N. Kawai (Tokyo Tech), H. Khandrika (STScI), A. Lien
(UMBC/GSFC), J. Lyman (Warwick), I. Mandel (Birmingham), P. O'Brien
(Leicester), J. Osborne (Leicester), E. Palazzi (INAF-IASF Bologna),
D. Perley (LJMU), E. Pian (INAF-IASF Bologna), L. Piro (INAF/IAPS),
T. Sakamoto (AGU), S. Schulze (Weizmann Institute of Science),
S. Rosswog (Stockholm), D. Steeghs (Warwick), P. Sutton (Cardiff),
D. Watson (DARK, Copenhagen) report:

We obtained both multi-wavelength imaging and spectroscopy of
the proposed counterpart (LVC GCN 21529
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 ) of LIGO/Virgo G298048 
(LVC GCN 21509
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 ) with the Hubble Space Telescope at several epochs 
between 22 and 28 August (under programmes GO 14804 (Levan), 
GO 14850 (Troja) and GO 14771 (Tanvir)). The transient is well 
detected in both the nIR and optical imaging, but is fading rapidly at the 
end of the observations, with a factor two fading between Aug 26 
and Aug 28 in the F160W filter.

Spectroscopy at the first epoch covers the range 0.9-1.6 microns,
and the counterpart is well detected across this spectral range.
The spectrum is dominated by a range of broad features, most notably
a peak at ~1.1 microns, but additional features are observed between
1.2 and 1.6 microns.

An image of the field, as observed by HST is shown at

http://www.astro.warwick.ac.uk/people/levan/gw_hst001

NOTE: The page is password protected with password HsT_G298048, and
the image should not be shared.

We thank the staff of STScI, in particular Patrica Royle, Alison
Vick, Neill Reid and Lou Strolger for their rapid work in scheduling
these ToO observations.

L. P. Singer (NASA/GSFC), R. Lau (Caltech), and M. M. Kasliwal (Caltech)
report on behalf of the Global Relay of Observatories Watching Transients
Happen (GROWTH) collaboration:

We report continued near-infrared observations in J, H, Ks band on the
FLAMINGOS-2 instrument on Gemini-South through 2017-08-31 UT. The source
seems to have ceased fading between 2017-08-28 UT and 2017-08-29 UT and
reached a plateau at about Ks = 17.7 mag (Vega).

E. Troja (UMD/GSFC), N. Butler (ASU), A. Watson (UNAM), S. Covino (INAF),
W. H. Lee (UNAM), J. Becerra-Gonzalez (UMD/GSFC), A. Lien (UMBC),
T. Sakamoto (AGU), and P. D'Avanzo (INAF):

We continued optical and near-infrared observations of SSS17a (Coulter et
al., LVC GCN 21529
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 ). The source appears substantially fainter than
in our previous observations ( Troja et al., LVC GCN 21682
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 ),
consistent with the rapid NIR fading reported by Chornock & Berger
(LVC GCN 21684
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 ).  However, over the course of the last three nights,
the NIR countepart appears to have flattened inthe Ks-band at
a level of ~17.7 mag.

We thank the entire Gemini-South staff and the director, Laura Ferrarese,
for their support of these observations.

[GCN OPS NOTE(31aug17): Per author's request, the middle sentence 
as added to the first paragraph.]

L. Resmi (IIST),  K. Misra (ARIES),  N. R. Tanvir (U. Leicester), P. T. O�Brien (U. Leicester) and S. Schulze (Weizmann Institute of Science) report on behalf of a larger collaboration.

We observed the LIGO/Virgo G298048 source SSS17a (Coulter et al. LVC GCN Circ. 21529
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 ) with the Giant Meterwave Radio Telescope (GMRT) on 25 Aug 2017 10.5 UT at 1390 MHz for a total integration time of 2 hours.  
 
Preliminary analysis of the data does not reveal any emission at the location of the optical transient up to a 3-sigma upper limit of 130 micro Jy. 
 
We report a weak detection of ~ 160 micro Jy at

RA(2000) = 13:09:47.74
Dec(2000) = -23:23:01.24  with a positional uncertainty of 3".   
This is consistent with the position of the optical host galaxy and the JVLA/ALMA radio source reported by Alexander et al. (LVC GCN Circ 21589
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 ) and Williams et al (LVC GCN Circ 21750
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 ). 

Further analysis is underway. Continued follow-up observations are planned.

We thank the GMRT staff for prompt scheduling of these observations. The GMRT is run by the National Center for Radio Astrophysics of the Tata Institute of Fundamental Research.

E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), T. Sakamoto (AGU),
S. B. Cenko (NASA/GSFC), and A. Lien (UMBC/GSFC) report on behalf
of a larger collaboration:

We observed the field of SSS17a (Coulter et al., LVC GCN 21529
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 ) with
the Chandra X-ray Observatory under our approved guest observer program
(18500489; PI: E. Troja). Observations were carried out on 2017-08-26
(~9 days after the LVC trigger) for a total exposure of 50 ks.

We detect the extended X-ray source visible in previous observations
(Evans et al., LVC GCN 21612
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 ; Margutti et al., LVC GCN 21648
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 ) at a
comparable flux level. In addition, we detect an X-ray source at the
optical/IR transient position, approximately 10 arcsecond from the
centroid of the extended X-ray emission. The probability to find an
unrelated X-ray source within the small localization of the optical
transient is negligible (<1E-5).

Previous candidate kilonovae (e.g. GRB080513, Perley et al. 2009;
GRB130603B; Tanvir et al. 2013) were associated to transient X-ray
emission, although bright X-rays are not a basic prediction of this
model. In our case, the properties of the X-ray emission and the
overall spectral energy distribution appear different.
The most likely explanation seems that the observed X-rays arise from
the afterglow of GRB170817A (Connaughton et al., LVC GCN 21506
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 ;
Savchenko et al., LVC GCN 21507
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 ), thus confirming the spatial
association between the short GRB and SSS17a.

A newborn spinning-down magnetar could power a long-lived and nearly
constant X-ray emission (Zhang & Meszaros, 2001). However,
the observed timescale and X-ray luminosity would imply unrealistic
values of the initial spin period and magnetic field. The previous
lack of detection from Chandra (Margutti et al., LVC GCN 21648
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 )
further disfavors this magnetar model. Other models (e.g. Metzger
& Piro, 2014) also do not match our observed luminosities and timescales.

For a standard on-axis afterglow, the extrapolation of the observed
flux would violate the upper limits reported by Evans et al.
(LVC GCN 21550
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 ), and Cenko et al. (LVC GCN 21572
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 ).

Our observations are instead consistent with the onset of an off-axis
afterglow from the GRB jet. This would explain the low luminosity of
the observed gamma-ray emission, and the lack of early afterglow
detections.

Further observations are planned.

We thank Belinda Wilkes and the entire CXC staff for rapidly scheduling
these observations.

Zsolt Paragi (JIVE)
Ivan Agudo (IAA Granada)
Tao An (Shanghai Astronomical Observatory)
Philippe Bacon (APC Universite�� Paris Diderot)
Rob Beswick (JBO-Manchester University)
Carolina Casadio (MPIfR-Bonn)
Eric Chassande-Mottin (APC Universite�� Paris Diderot)
Sa��ndor Frey (Konkoly Observatory)
Marcello Giroletti (IRA-INAF)
Peter Jonker (SRON)
Mark Kettenis (JIVE)
Benito Marcote (JIVE)
Arpad Szomoru (JIVE)
Huib van Langevelde (JIVE)
Jun Yang (Onsala Space Observatory)
for the Euro VLBI team

We observed SSS17a (Coulter et al. LVC GCN  21529
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 ) at 5 GHz with
the European VLBI Network between 12:15���16:15 UT on 26 August 2017.
Preliminary analysis shows no compact radio emission detectable on
milliarcsecond angular scales above 160 microJy (~5 sigma) in a
1.6 x 1.6 arcsec region. Further observations are planned.


The EVN is a joint facility of independent European, African, Asian,
and North American radio astronomy institutes. Scientific results
from data presented in this publication are derived from the following
EVN project code: RP029.



-- 
Zsolt Paragi
Head of User Support

Joint Institute for VLBI ERIC (JIVE)    Web:  http://www.jive.eu
Oude Hoogeveensedijk 4                  Phone:  +31 (0)521-596-536
7991 PD  Dwingeloo                        Mobile:  +31 (0)629-034-718
the Netherlands                                Fax:  +31 (0)521-596-539

T. J. Pearson and A. C. S. Readhead (Caltech) on behalf of the Owens Valley
Radio Observatory.

The KuPol receiver on the Owens Valley Radio Observatory 40m telescope is a
dual-beam switched radiometer with a resolution ~ 3 arcmin operating in the
13-18 GHz band (http://www.astro.caltech.edu/ovroblazars/).

We observed the candidate counterpart SSS17a and NGC 4993 at the following
times (UTC):

2017-08-19T21:57:46 to 2017-08-20T01:38:52
2017-08-23T21:18:44 to 2017-08-24T00:10:30

On-off measurements of about 32s on-source integration were inerleaved with
calibration observations, for a cadence of roughly 15 measurements per hour.

In both periods there was no signal above our 3-sigma detection limit ~ 50
mJy in any individual on-off measurement.

Further observations are planned, along with improved analysis to refine
the upper limit.

P. K. G. Williams (Harvard), K. D. Alexander (Harvard), and E. Berger
(Harvard) report on behalf of a larger collaboration:

We observed the position of the optical counterpart SSS17a (Coulter et al., LVC 21529) with the Atacama Large Millimeter/submillimeter Array
(ALMA) on 2017 August 19 UT and 2017 August 26 UT. Each observation
lasted 20 minutes and was performed using ALMA's Band 3, with spectral
windows of 4 GHz bandwidth centered at 91.5 and 103.5 GHz. 

We have analyzed the data using a custom CASA-based pipeline. At a mean
frequency of 97.5 GHz, we detect no emission at the location of the
optical transient to a combined 3-sigma limit of 50 microJy. We detect
a source with a preliminary flux density of ~0.2 mJy at the location:

RA = 13:09:47.696
dec = -23:23:02.31

with a positional uncertainty of ~0.04 arcsec. This is consistent with
the optical position of the host galaxy and the position of the radio
source reported by Alexander et al. (LVC 21545) and others.

We thank the ALMA staff, especially Tony Remijan, for their excellent
support.

S. Schulze (Weizmann Institute of Science), S. Kim (PUC Chile), S. Martin (JAO), F. E. Bauer (PUC Chile), M. Bremer (IRAM), S. Campana (INAF Brera), Z. Cano (IAA Granada), J. Corral-Santana (ESO Chile), P. D'Avanzo (INAF Brera), C. De Breuck (ESO), I. de Gregorio-Monsalvo (JAO), M. de Pasquale (Istanbul University), J. P. U. Fynbo (Dark Cosmology Centre), D. Garcia-Appadoo (JAO), D. Hartman (U. Clemson), J. Hjorth (Dark Cosmology Centre), P. Jakobsson (U. Iceland), D. A. Kann (IAA Granada), T. Kruehler (MPE Garching), R. Lekshmi (ARIES), A. J. Levan (U Warwick), A. Lundgren (JAO), D. Malesani (Dark Cosmology Centre), M. Michalowski (Adam Mickiewicz University), B. Milvang-Jensen (Dark Cosmology Centre), K. Misra (ARIES), S. R. Oates (U. Warwick), R. Sanchez-Ramirez (IAA Granada), M. Sparre (Heidelberg Institute for Theoretical Studies), R. L. C. Starling (U. Leicester), N. R. Tanvir (U. Leicester), C. C. Thoene (IAA Granada) and D. J. Watson (Dark Cosmology Centre) report:

We have used the Atacama Large Millimeter/submillimeter Array, ALMA, to observe the field of LIGO/Virgo candidate G298048 (The LIGO Scientific Collaboration and the Virgo Collaboration GCN Circ. 21509
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 ) and GRB 170817A (Connaughton et al. GCN Circ. 21506
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 ; Svinkin et al. GCN Circ. 21515
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 ), centered on the position of the optical transient reported in Coulter et al. (GCN Circ. 21529
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 ).

Observations were taken at four epochs: 2017-08-18, 2017-08-20, 2017-08-21 and 2017-08-25 and have been carried out in the B7 band centred at 338.5 GHz (central wavelength 0.89 mm). The field of view covered an area of 18.3 arcsec. Data processing is underway.

We thank ALMA for their excellent support.

D. Svinkin, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

Konus-Wind (KW) was observing the whole sky at the time of the 
LIGO/Virgo event G298048 (2017-08-17 12:41:04.446 UTC, hereafter T0; 
LIGO/Virgo Collaboration GCN Circ. 21509
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 ) coincident with Fermi GBM 
trigger 524666471 (Connaughton et al., GCN Circ. 21506
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 , Goldstein et 
al., GCN Circ. 21528
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 ).

Using waiting-mode data within the interval T0 +/- 100 s,
we found no significant (> 4 sigma) excess over the background
in both KW detectors on temporal scales from 2.944 s to 100 s.

For the 2.944 s interval containing GBM trigger and the 
highest-probability localization region for the LIGO/Virgo G298048 (LVC, 
GCN Circ. 21513
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 ) we estimate an upper limit (90% conf.) on the 10 keV ��� 
10 MeV fluence to 3.0x10^-7 erg/cm^2 for a burst lasting less than 2.944 
s and having the spectrum reported by Goldstein et al. (an exponentially 
cut off power law, CPL, with alpha=-0.9 and Ep=128 keV).
For a typical short GRB spectrum (CPL with alpha=-0.5 and Ep=500 keV), 
the limiting fluence is 6.9x10^-7 erg/cm^2 (10 keV ��� 10 MeV).

All the quoted values are preliminary.

D. Coward (UWA), E. Howell (UWA), R. Laugier (ARTEMIS - CNRS/UCA/OCA), A. Klotz (IRAP - CNRS/UPS), M. Boer, (ARTEMIS - CNRS/UCA/OCA),  I. Andreoni (Swinburne), J. Cook (Swinburne), D. Macpherson (UWA), J. Moore (UWA) and A. Burrell (UWA) report on behalf of OzGrav and TZAC (see acknowledgements below):

We report 7 days of Zadko Telescope imaging of the transient SSS17a/DLT17ck in NGC4339 started on 2017-08-19 10:57 UT (t0+2 days).

We use the stacked image of the night 201-08-26 (t0+9 days) as a mask to substract the light contribution from the galaxy NGC 4993 and synthesise one residual image for each nights observation. Photometry is performed using the star NOMAD-1 0666-0296321 for PSF fitting.

The complete log of Zadko image analysis from t0+2 ��� t0+9 is:

Tstart 	Tend 	r(AB) 	1sigma
1.928 	1.930 	18.46 	0.17
2.929 	2.950 	19.18 	0.12
3.941 	3.974 	19.86 	0.21
4.955 	4.964 	20.20 	0.23
5.953 	5.973 	>20.6
6.958 	6.978 	>20.6
7.955 	7.976 	>20.6

Observations are compatible with a power law decay (alpha=-2) or with a exponential decay with a half time of 1.25 days.

The Zadko Telescope is operated by the University of Western Australia (UWA), and was made possible by a philanthropic donation by James Zadko, to UWA.

Zadko Telescope receives support from the ARC Centre of Excellence ���OzGrav��� for gravitational wave follow-up and discovery. The facility is managed by D.Coward (Director-UWA), E. Howell (UWA), J. Moore (UWA), A. Burrel (UWA), A. Greensky, J. Kennewell with collaborators I. Andreoni and J. Cook (Swinburne)

This observation report was done in partnership with the LIGO follow-up collaboration TZAC, which is supported by M. Boer, A. Klotz, R. Laugier, K. Noysena

C. Lynch (University of Sydney), T. Murphy (University of Sydney),
D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney)
on behalf of the VAST collaboration.

Following Lynch et al. (LVC GCN 21670
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 ), we observed a third epoch of
NGC 4993 with the Australia Telescope Compact Array at 8.5 and 10.5 GHz.
Observations started at 2017-08-27 23:26:24.9 UT and ended at
2017-08-28 9:00:00 UT with approximately 2.3 hours of on-source time.

We fit and subtracted a point-source at the optical position of NGC 4993
(13:09:47.71, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source
Catalog). From this we set a 3-sigma upper limit of 54 uJy and 39 uJy on
radio emission from SSS17a at 8.5 and 10.5 GHz respectively.

Subsequent epochs are planned.

Thank you to CSIRO staff for supporting these observations.

K. De (Caltech), K. P. Mooley (Oxford), P. Chandra (NCRA), V. Bhalerao
(IIT-B), A. Corsi (TTU), D. Kaplan (UWM), G. Hallinan (Caltech) and M. M.
Kasliwal (Caltech)

report on behalf of the GROWTH (Global Relay of Observatories Watching
Transients Happen) collaboration

We report on continued follow-up observations of SSS17a (GCN 21529
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 ; Coulter
et al.) with the upgraded Giant Metrewave Radio Telescope (uGMRT) following
the first epoch at 610 MHz (GCN 21603
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 ; De et al.). Observations were
carried out on UT 20 August 2017 08:00 at 400 MHz (200 MHz bandwidth) for
an on-source time of ~ 1 hour and on UT 20 August 2017 11:00 at 1.4 GHz
(400 MHz bandwidth) for an on-source time of ~ 2 hours.

After a preliminary analysis, no emission is detected at the location of
the optical transient at 1.4 GHz up to a 3 sigma upper limit of 100
microJy. The transient was also undetected at 400 MHz, although this
observation was partially affected by RFI and the analysis is being
improved. Further multi-frequency observations are planned.

We thank the GMRT staff for prompt scheduling of these observations. The
GMRT is run by the National Center for Radio Astrophysics of the Tata
Institute of Fundamental Research.

A. Grado (INAF-OAC), F. Getman (INAF-OAC), L. Limatola (INAF-OAC), E.
Cappellaro (INAF-OAPD), M. Branchesi (GSSI), S. Covino
(INAF-OAB), P. D'Avanzo (INAF-OAB),  A. Melandri (INAF-OAB), L. Amati
(INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S.
Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC),  S. Campana (INAF-OAB), V.
D'Elia (INAF-ASDC), D. Fugazza, M. Lisi (INAF-OAR), G. Greco (Urbino
University/INFN Firenze), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS
Bo), E. Pian (INAF-IASF Bo), S. Piranomonte (INAF-OAR), L. Pulone
(INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Stratta
(Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa
(INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato
(INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report:


Observations of 1 square degrees of the skymap of the Advanced LIGO and
Virgo trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) were performed with the
VLT Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal
equipped with OMEGACAM (FOV=1 square degree). The observations cover the
galaxy NGC4993.
The images were acquired with the g_SDSS, r_SDSS, i_SDSS, z_SDSS filters
for a total exposure of 200s in each filter. The observations started at
2017-08-22T 23:09:27.845 UTC and finished at 2017-08-23T 23:45:38.546 UTC.
The optical counterpart at RA=13:09:48.09 DEC=-23:22:53.35 reported by
Coulter et al. (LVC GCN 21529
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 ), Allam et al. (LVC GCN 21530
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 ), Yang et al.
(LVC GCN 21531
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 ), Melandri et al. (LVC GCN 21532
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 ) and several others authors
is visible in the gri filters with AB magnitudes of 23.3, 22.4 and 21.3
respectively, while is not visible in the z band.
Automatic data reduction with the VSTTube pipeline (Grado et al. 2012
Mem.SAIt 19, 362 ) was completed.
We acknowledge excellent support from the ESO User Support Department, in
particular G. Beccari, and from ESO observing staff in Paranal.

V.M.Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, 
P.Balanutsa,  O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov
Lomonosov Moscow State University, Sternberg Astronomical Institute

R.Podesta, C.Lopez, F.Podesta
Observatorio Astronomico Felix Aguilar (OAFA) , National University of San
Juan, Argentina

H.Levato, C.Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina

D.Buckley, S.Potter, M.Kotze,
South African Astronomical Observatory

N.M. Budnev, O. Gress, K. Ivanov, S.Yazev
Irkutsk State University

V.Yurkov, Yu.Sergienko, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu
The Instituto de Astrofisica de Canarias

A. Tlatov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

MASTER Global Robotic Net (http:/ / observ.pereplet.ru/ ) consists of a 
new generation of fast robotic telescopes that
installed on different continents during recent years.

MASTER-II are twin 40 cm wide field (2x4 square degrees, 1 pixel = 2.0 
arcsec) optical robotic telescopes located in the following observatories:
MASTER-Amur (far east of Russia, Blagoveshchensk), MASTER-Tunka (Russia, 
Baykal lake), MASTER-Kislovodsk, MASTER-Tavrida (Russia), MASTER-SAAO (South Africa), 
MASTER-IAC (Spain, Canarias), and MASTER-OAFA (Argentina, MASTER I yet).

MASTER observatories are equipped with their own identical photometers and 
are controlled by identical software (Lipunov et al., "MASTER Global 
Robotic Net",  Advances in Astronomy, 2010, 30L).

  The identical equipment gives us the possibility of having up to  24 
continuous hours observations of optical counterparts of GRBs in identical
photometric systems. Therefore, combining photometric data for different 
GRBs observed from different parts of the MASTER Net is a well-justified 
astronomical process (see last result in Troya, Lipunov, Mundel  et al., 
Nature, 2017, vol.547,425-427)

Taking into account the large field of view of the MASTER II telescopes (8 
square degrees), we can use a large number (1000 - 5,000)
of reference stars for reduction. As a result, the photometric errors of 
large catalogs, Tycho II and   USNO-B1, shouldbe leveled out.

Global MASTER-Net started to observe LIGO/Virgo G298048 error field at 
2017-08-17 17:06:47 UT.

MASTER-SAAO (MASTER II robotic telescope at South Africa Astronomical 
Observatory, Sutherland) automaticaly have imaged the initial BAYESTAR error 
field received by socket connection (LVC GCN 21505
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 ) including
common region with Fermi GBM error box  (Connaughton  et al., LVC GCN 21506
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 ) 
immediatelly after sunset  at 2017-08-17 17:06:47 = 2017-08-17.71304 (JD = 
2457983.21304398) i.e. 15943 sec after LVC trigger time (12:41:04 UT) .
 	The coaadded (3x180sec) first   unfiltered images limit is 19.8. This 
image  included ICECube candidate N4   (Bartos et al  LVC GCN 21511
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 ). No OTs 
found  in this error box.

After that MASTER-SAAO telescope continue to image Fermi and LVC initial common 
error field and all Ice Cube candidates. The unfiltered limits and fields 
one can find at GraceDB. Cover map is available at
http://master.sai.msu.ru/static//ligo/db/G298048/151A//img/MASTER.G298048.180.24.gif

No OTs found at this observations.
The Possible KiloNova SSS17a in NGC 4993 (Coulter et al., LVC GCN 21529
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 ) 
is  not covering by MASTER-SAAO at 17 Aug 2017.

MASTER-OAFA  (MASTER I robotic telescope with FOV = 6 square degrees;  at Argentina, Observatorio Astronomico Felix Aguilar 
(OAFA), National University of San Juan,) have imaged the new BAYESTAR-HLV
localization map of  LIGO/Virgo  G298048 (GCN 21513
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 ) starting
2017-08-17 22:54:18 =  2017-08-17.954375 from  first field (6 square degrees):

RA, DEC  = 12h 59m 00.00s -19d 59m 38.00s

Unforunatelly the first telescope image not include sss17a.

But fortunally 
there are two MASTER Very Wide Field cameras (FOV = 2x380 square degrees, 
22 arcsec in pixel, see Lipunov et al.,  2010, MASTER Robotic Net, 
Advances in Astronomy, vol. 2010, pp. 1-7)  at same mount.
As the results we have large seria ("video") MASTER VWF cameras images 
exposition and without time gap of the all LIGO/Virgo G298048 error box include 
the NGC 4993 galaxy. We see NGC 4993 galaxy on coadded images. After the 
images substraction with refernce very wide field camera images we see 
some excess (see Table 1) at NGC 4993 position with flux corresponded to ~15.3 
mag.

Starting from 2017-08-17 22:58:48 UT = 2017-08-17 22:58:48 MASTER-OAFA have 
imaged  new BAYESTAR-HLV localization map of  LIGO/Virgo  G298048 (GCN 21513
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 ) 
with unfiltered images (150 sec exposition) limit 19-20 magnitudes. The coadded 
images limit grows to 20.5.

At 2017-08-17 23:59:54 UT   i.e. 11 h 18m 50 sec after LVC trigger time 
MASTER-OAFA robotic telescope independently from any optical 
information take second image with NGC 
4993 galaxy where Possible KiloNova SSS17a was published late
Coulter et al., LVC GCN  21529
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 , Allam et  al. (LVC GCN 21530
Loading...
 
 ), Yang et al. 
(LVC GCN 21531
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 ), Melandri et al.  (LVC GCN 21532
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 ),
Lipunov et al., (LVC GCN 21546
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 ), Chen et al. (LVC GCN 21608
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 ).

On the next 3 days both southern MASTER robotic telescopes at SAAO and OAFA was 
done (and continue now) B,R, Unfiltered monitoring Possible KiloNova SSS17a at 
NGC 4993 galaxy.

The covering video map at first day is available at 
http://master.sai.msu.ru/static//ligo/db/G298048/151//img/MASTER.G298048.180.24.gif

The photometry of sss17a listed at  Table I. This photometry made 
by substracted images and free from galaxy background.

TableI. MASTER Global Robotic Net the sss17a photometry
-----------------------------------------------------------------------
    Date      UT     T-Ttrig   Exp Filt   Mag  Err  Lim   Instr      SITE
             start   Kilosec   sec

2017-08-17 22:54:18  36.794  225x5  V   15.3* 0.5  15.5 MASTER VWFC OAFA
2017-08-17 23:59:54  40.730   180   W   17.7  0.2  19.5 MASTER I    OAFA
2017-08-18 00:19:05  41.881   180   W   17.3  0.2  19.3 MASTER I    OAFA

2017-08-18 17:06:55 102.352  6x180  W   17.5  0.2  20.0 MASTER II   SAAO
2017-08-18 17:17:33 102.989  3x180  R   17.2  0.2  19.8 MASTER II   SAAO
2017-08-18 17:34:02 103.979  3x180  B   18.5  0.1  19.5 MASTER II   SAAO

2017-08-19 17:06:57 188.753  3x180  W   18.6  0.2  20.0 MASTER II   SAAO
2017-08-19 17:53:34 191.550  3x180  R   18.2  0.3  19.8 MASTER II   SAAO
2017-08-19 18:04:32 192.208  3x180  B   ----  ---  19.5 MASTER II   SAAO
2017-08-19 23:13:20 210.736 10x180  W   19.0  0.2  20.7 MASTER I    OAFA

2017-08-20 17:04:36 275.012  3x180  W  >19.3  ---  20.0 MASTER II   SAAO
2017-08-20 17:25:56 276.292  3x180  R  >18.8  ---  19.5 MASTER II   SAAO
2017-08-20 17:36:32 276.928  3x180  B  >19.7  ---  20.0 MASTER II   SAAO
2017-08-21 00:26:31 301.527 10x180  W  >20.0   --- 20.7 MASTER I    OAFA

2017-08-21 17:08:14 361.630  3x180  W  >19.3  ---  20.0 MASTER II   SAAO
2017-08-21 18:06:12 365.108  3x180  R  >18.8  ---  19.5 MASTER II   SAAO
2017-08-21 19:20:23 369.559  3x180  B  >18.7  ---  19.0 MASTER II   SAAO


-----------------------------------------------------------------------
* This is a photometry of some faint excess on substracted image. It is 
possible to be a image substraction noice.

Ttrig - LVC trigger Time
T - is the exposition start time
W - unfiltered
VWFC - Very Wide Field Camera





Table 2. Start and midle times.

---------------------------------------------------------
    Date      UT              JD         UT
            start            start      midle

2017-08-17 22:54:18    2457983.454   23:03:40
2017-08-17 23:59:54    2457983.4999  00:01:24
2017-08-18 00:19:05    2457983.513   00:20:35

2017-08-18 17:06:55    2457984.217   17:11:57
2017-08-18 17:17:33    2457984.226   17:25:27
2017-08-18 17:43:02    2457984.236   17:39:14

2017-08-19 17:06:57    2457985.213   17:11:52
2017-08-19 17:53:34    2457985.246   17:58:29
2017-08-19 18:04:32    2457985.253   18:09:27
2017-08-19 23:13:20    2457985.468   23:30:50

2017-08-20 17:04:36    2457986.212   17:09:31
2017-08-20 17:25:56    2457986.226   17:30:51
2017-08-20 17:36:32    2457986.234   17:41:27
2017-08-21 00:26:31    2457986.518   00:44:01

2017-08-21 17:08:14    2457987.214   17:13:09
2017-08-21 18:06:12    2457987.254   18:11:07
2017-08-21 19:20:23    2457987.306   19:25:18
---------------------------------------------------

There are MASTER-NET 126 arhival images of the NGC 4993 galaxy
since 2015-01-17 00:45:46 till 2017-05-02 22:17:04 .
No optical sss17a activity was found.
The MASTER arhival images table is available at
http://master.sai.msu.ru/static/MASTER_G298048_PREDISCOVERY1.txt .


As the discussion about physical nature GW 170817/G298048 (Lipunov, LVC GCN 
21621
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 ; Nichol etal., LVC GCN 21585
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 ,  LVC GCN 21592
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 ; D'Elia et al.,LVC GCN 21592
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) I (Vladimir Lipunov) would like to point that distance of the binary NS 
merging ~ 40 Mpc is in good agreement with predicted merging rate inside local 
super cluster (Lipunov, Postnov & Prokhorov, 1987, A&A, vol.176, L1-L4.). See 
fig. 1 which is vailable at http://master.sai.msu.ru/static/LPP1987_fig1.jpg .

There was predicted 1 merging NS+NS per year for 20 Mpc radius volume(e-case, 
see capture). This means, that for 40 Mpc  predicted ~ 10 per year!

This message can be citted.

J. Alvarez-Muniz, F. Pedreira, E. Zas (Univ. Santiago de Compostela, Spain),
K. H. Kampert & M. Schimp (Bergische Universitat, Wuppertal, Germany)
on behalf of the Pierre Auger Collaboration.

In response to:
LIGO/Virgo GW trigger G298048
(GCN #21505
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  and #21509
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  ,T0=2017-08-17 at 12:41:04.527 UTC)

We searched for Ultra-High-Energy (UHE) neutrinos with energies
above ~ 1e17 eV in data collected with the Surface Detector (SD)
of the Pierre Auger Observatory in a [-500,500] second interval
about the LIGO-Virgo trigger G298048 as well as 1 day after it.

The field of view (fov) where the SD of Auger is sensitive to UHE
neutrinos (corresponding to inclined directions with respect to the
vertical relative to the ground) was FULLY COINCIDENT with the
LIGO+Virgo 90% localization region (GCN #21513
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  bayestar-HLV.fits.gz)
at the time T0 of the merger alert as well as with the optical
counterpart detected by the Swope telescope (GCN #21529
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 ).
Also the 90% CL Fermi GBM trigger 170817.529 contour (GCN #21506
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 )
at the trigger time was largely overlapping with the Auger fov.

NO events survived the cuts applied to reject the background due
to UHE Cosmic Rays i.e. NO neutrino candidates were detected.

-------
The Pierre Auger Observatory is an UHE Cosmic Ray detector
located in the Mendoza Province in Argentina. It consists of
an array of Water Cherenkov detectors spread over a total surface
of 3000 km^2 arranged in a triangular grid of 1.5 km side as well
as Fluorescence telescopes and other systems
(see 10.1016/j.nima.2015.06.058 for more information).
For neutrino searches from GW events with Auger, please refer to:
https://journals.aps.org/prd/pdf/10.1103/PhysRevD.94.122007

Yoshida, M., Tanaka, M. (NAOJ), Utsumi, Y. (Hiroshima Univ.),
Tominaga, N. (Konan Univ.), Ohsawa, R., Motohara, K. (Univ. of
Tokyo), Terai, T., Nakata, F., Lee, C. H., Furusawa, H., Koshida,
S. (NAOJ), Ohta, K. (Kyoto Univ.), Kawabata K. S. (Hiroshima
Univ.), Morokuma, T., Yasuda, N. (Univ. of Tokyo), Kawai, N.
(Tokyo Tech.), and Asakura, Y. (Nagoya Univ.) on behalf of the
J-GEM collaboration

We have performed z-band imaging observations of the OT candidate
of G298048, SSS17a (Coulter et al., GCN 21529
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 ) with Hyper
Suprime-Cam attached to the Subaru telescope on August 25.2 2017
UT. We found that the z-band magnitude of the source was
significantly fainter compared to our previous observations on
August 19.2 2017 UT (Yoshida et al. GCN 21586
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 ; Tominaga et al.
GCN 21595
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 ). Further analysis is ongoing.

R. Chornock (Ohio University) and E. Berger (Harvard) report on behalf of a 
larger collaboration:

Further to our previous report (LVC GCN 21638
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 ), we have continued near-infrared 
observations of the optical counterpart (Coulter et al., LVC GCN 21529
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 ; Allam et 
al., LVC GCN 21530
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 ; Yang et al., LVC GCN 21531
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 ) to the LIGO/Virgo source G298048 
(GCNs 21509
Loading...
 
 , 21513
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 ) using FLAMINGOS2 on Gemini-South (PI: Chornock).

Over the course of our initial observations, obtained during the first 4.5 days 
after the GW trigger, the H-band flux from the near-infrared source was not 
strongly variable.  However, in H-band acquisition images obtained tonight 
(20170824 at 23:47 UT, t~7.5 d after the GW trigger), the NIR counterpart 
appears substantially fainter (by >1 magnitude) compared to our previous 
observations three nights earlier.  A phase of more rapid NIR fading may have begun.

We thank the entire Gemini-South staff, but particularly H. Kim, G. Diaz, J. 
Chavez, P. Candia, and the director, Laura Ferrarese, for their support of these 
observations.

I. Martinez-Castellanos (University of Maryland, College Park) and
A.J. Smith (University of Maryland, College Park) on behalf of the
HAWC Collaboration:

HAWC Collaboration performed a follow-up of LIGO trigger G298048. At the
time of the trigger no portion of the LV contour was visible to HAWC, so
no prompt follow-up was possible.

About 9hrs after the trigger the LV region transited through the HAWC FOV
(95% of the probability was covered), albeit with a large zenith angle,
which limits the sensitivity of our observations. There were no >5 sigma
points observed during this transit. For a single transit, the 5 sigma
sensitivity to a power law spectrum with a -2.5 index ranges from
~2e-11 >1TeV cm^-2 s^-1 (~3 Crab units) at dec=-12 to about 6 times higher
at the edge of our FOV, dec=-25.

At the point of the optical counterpart candidate SSS17a/DLT17ck
(RA=13:09:48.09 DEC=-23:22:53.35) reported by Coulter et al. (LVC GCN
21529
Loading...
 
 ), Allam et al. (LVC GCN 21530
Loading...
 
 ), Yang et al. (LVC GCN 21531
Loading...
 
 ),
Melandri et al. (LVC GCN 21532
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 ), we obtain an 95% confidence level upper
limit for >1TeV assuming a -2.5 spectrum of 1.0e-10 cm^-2 s^-1. These
observations were made on 2017-08-17 between 19:57 UT and 23:25 UT with
culmination 9:00 hrs after the LV trigger.

HAWC is a TeV gamma ray water Cherenkov array located in the state of
Puebla, Mexico. It is sensitive to the energy range ~0.5-100TeV, and
monitors 2/3 of the sky every day with an instantaneous field-of-view of
~2 sr.

E. Troja (UMD/GSFC), A. Watson (UNAM), S. Covino (INAF), W. H. Lee (UNAM),
N. Butler (ASU), J. Becerra-Gonzalez (UMD/GSFC), A. Lien (UMBC),
T. Sakamoto (AGU), and P. D'Avanzo (INAF)

and

L. P. Singer (NASA/GSFC), C. Fremling (Caltech), and M. M. Kasliwal
(Caltech) on behalf of the GROWTH (Global Relay of Observatories
Watching Transients Happen) collaboration report:

We observed the field of the transient SSS17a in NGC 4993 (Coulter
et al. 2017; GCN 21529
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 ) with the Flamingos-2 (F2) instrument and
the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini-
South 8-m telescope starting on 2017 Aug 20.98 UT, ~3.5 days after
LIGO/Virgo trigger G298048 (LVC GCN Circ. 21509
Loading...
 
 , 21513
Loading...
 
 ). Imaging
observations were carried out in the g, r, i, z, J, H and K filters.
The source is detected in all bands with a preliminary magnitude J~17.2.
We also obtained a pair of 1200s GMOS spectra with the R400 and the B600
gratings. We do not detect any significant emission or absorption lines
over the red featureless continuum.

We thank the Gemini staff, particularly Hwihyun Kim, Ricardo Salinas,
and Laura Ferrarese for their support of these operations.

A.J. Levan, J.D. Lyman, D.T.H. Steeghs (U. Warwick), N.R. Tanvir (U. Leicester), J. Hjorth (Dark Cosmology Centre) report on behalf of a larger collaboration:

"We observed the candidate counterpart and host galaxy (NGC 4993) of LIGO/Virgo G298048 (LSC GCN 21509
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 ) with the ESO VLT and the MUSE Integral Field Unit, starting at 2018 August 18.99. MUSE has a 1��� field of view, and a spectral range from 4650-9300A. Both the host galaxy and transient are clearly visible. The bulk spectrum of the transient is comparable to others reported at the same epoch (Lyman et al. GCN 21582
Loading...
 
 , Nicholl et al. GCN 21585
Loading...
 
 , D���Elia et al. GCN 21592
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 ).

The galaxy is dominated by a spheroidal component, but weak spiral arms can be seen in emission lines extending both north and south from the centre of the galaxy. They do not reach the location of the transient, and no underlying star formation in the form of emission lines is evident in the vicinity of the transient source. Further analysis is ongoing.

We thank the staff at Paranal for their excellent assistance in performing the observations."

T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech),
M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U
Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J.
Tsai, C. Yancey (U Maryland)

The Long Wavelength Array (LWA1, located west of Socorro, New Mexico)
[S.W. Ellingson, et al. http://lanl.arxiv.org/abs/1204.4816] made
observations on June 17 following the LIGO trigger G298048. The first
observation began at 2017-08-17 13:09:51 UTC (28 minutes after the
trigger) and ran for approximately 1.1 hours.

All observations were centered at frequencies 25.85 MHz and 45.45 MHz,
each with a bandwidth of 19.6 MHz. The FWHM is 15.499 degrees at 25.85
MHz, and 6.648 degrees at 45.45 MHz.

The beam centers for the first observation were: Beam 1: RA 2.391h, Dec
41.810deg; Beam 2: RA 2.431h, Dec 46.572deg; Beam 3: RA 2.803h, Dec
44.202deg; and Beam 4: RA 2.660h, Dec 50.480deg. These were chosen to
observe the maximum of the LIGO skymap available with the initial
notice.

The next observation, using an updated skymap, began at 2017-08-17
19:15:00 UTC (6.6 hours after the trigger) and ran for 4 hours.

The beam centers for the second observation were Beam 1: RA 12.814h, Dec
-13.862deg; Beam 2: RA 12.955h, Dec -17.896deg; Beam 3: RA 13.096h, Dec
-22.024deg; and Beam 4: RA 11.786h, Dec -39.840deg. These coordinates
include the position of the observed transient, as reported by D.A.
Coulter, et al., [GCN 21529], as well as nearby regions.

We plan to continue follow-up observations at the second set of
coordinates over the next few weeks. Data analysis is proceeding.

I. Andreoni (Swinburne),  J. Cooke (Swinburne) on behalf of OzGrav
and
C. Lidman,  E. Elmer and T. Farrell  (AAO)


We performed spectroscopic observations of the GW counterpart candidate
SSS17a/DLT17ck (Coulter et al., LVC GCN 21529
Loading...
 
 ; Allam et al., LVC GCN 21530
Loading...
 
 ;
Sheng Yang et al., LVC GCN 21531
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 ) with the AAOmega spectrograph at the 4m
Anglo-Australian Telescope.

The AAOmega spectrograph covers a wavelength range 3700-8800 AA with a
resolution R=1700. 

We obtained 4 usable exposures of 600s each, starting at 2017-08-24.037 UT.

A preliminary analysis shows a red, largely featureless spectrum with no
obvious features other than host galaxy absorption lines.

J.W. Broderick (ASTRON), A. Rowlinson (UvA, ASTRON), P.G. Jonker (SRON, RU), R.P. Fender (Oxford), R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester), S. ter Veen (ASTRON), S. Nissanke (RU) and A. Shulevski (ASTRON) report on behalf of the LOFAR Transients Key Science Project

On 2017 August 22, we conducted a LOFAR follow-up observation of the Advanced LIGO/Virgo trigger G298048 with the ILT (International Low-Frequency Array [LOFAR] Telescope). This is a highly experimental observation to assess whether images of sufficient quality can be obtained at very low elevations. The observation began at 14:05:00 UTC, near transit, with any useable data likely only within the first hour. We placed two beams on the most northerly part of the probability distribution, as determined from the preliminary LALInference map. The bandwidth for each beam is 47.5 MHz, spread over the frequency range 120-187 MHz. The beam centres (RA/Dec), in degrees, are as follows:

1) 192.4167   -15.8333
2) 193.1875   -17.0000

where the field of view per beam is 11.35 deg^2 at 150 MHz. Analysis is ongoing, with the possibility of further observations if this test run is deemed to have been successful.  
  
We thank the ASTRON Radio Observatory for rapidly scheduling the observations.

M. de Naurois on behalf of the H.E.S.S. collaboration

The H.E.S.S. array of imaging atmospheric Cherenkov telescopes was used to carry out follow-up observations of the GW trigger G298048 (GCN #21509
Loading...
 
 ) and monitoring of the possible counterpart SSS17a/DLT17ck (Coulter et al. GCN #21529
Loading...
 
 ; Yang et al., GCN #21531
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 ).
H.E.S.S. observations started August 17 at 18:00 UTC with three pointings derived from the HLV-Bayestar map (GCN #21513
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 ) without assumptions on the orientation of the system and cross correlated in three dimensions with the GLADE catalog [1]. The first of these pointings covered the region of NGC 4993 and the potential EM counterpart SSS17a/DLT17ck. We continued to monitor the region around SSS17a/DLT17ck during the following nights until the location moved outside the H.E.S.S. visiblity window. The last pointing was taken August 22, 18:00 UTC.
Each of our observations has a sensitivity of about 20% of the flux from the Crab nebula at 5 sigma. A preliminary analysis with an energy threshold of about 500GeV did not reveal significant gamma-ray emission in any of the datasets. Further analyses of the data are on-going.

H.E.S.S. is an array of five imaging atmospheric Cherenkov telescopes for the detection of very-high-energy gamma-ray sources and is located in the Khomas Highlands in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, the Czech Republic, France, Germany, Ireland, Netherlands, Japan, Poland, South Africa, Sweden, UK, and the host country, Namibia. For more details see https://www.mpi-hd.mpg.de/hfm/HESS/

[1] GLADE website: http://aquarius.elte.hu/glade/

V. Savchenko (ISDC, University of Geneva, CH)
C. Ferrigno, E. Bozzo ((ISDC, University of Geneva, CH),
E. Kuulkers (ESTEC/ESA, The Netherlands),
S. Mereghetti (IASF-Milano, Italy),
T. J.-L. Courvoisier (ISDC, University of Geneva, CH)
J. Chenevez, S. Brandt (DTU, Denmark)
R. Diehl (MPE-Garching, Germany)
L. Hanlon (UCD, Ireland)
P. Laurent, D. Gotz (APC, Saclay/CEA, France)
J.P. Roques, E. Jourdain (IRAP, France)
P. Ubertini, A. Bazzano, J. Rodi (IAPS-Roma, Italy)
A. Lutovinov, R. Sunyaev (IKI, Russia)

INTEGRAL is an observatory with multiple instruments: a gamma-ray
spectrometer (20 keV - 8 MeV, SPI), an imager (15 keV - 2 MeV, IBIS),
an X-ray monitor (3 - 25 keV, JEM-X), and an optical monitor (V band,
OMC). Our group requested and obtained follow-up observations of the
LIGO/Virgo candidate NS merger G298048 (GCN 21505
Loading...
 
 , 21506
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 ).

The initial observation was centered on the best Fermi/GBM
localization, RA=176.8, Dec=-39.8 (GCN 21509
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 ), and was carried out
from 2017-08-18 08:17:51 to 2017-08-18 12:36:11 for a total observing
time of 14.8 ks. It covered 72% of the Fermi/GBM localization
probability but only a negligible fraction of the current LIGO/Virgo
localization. We do not detect any new sources in the complete
IBIS/ISGRI (20-80 keV and 80 - 300 keV) and JEM-X (3-10 keV, 10 - 25
keV) mosaicked images, with a best sensitivity of 7.9 mCrab (1.2e-7
erg/cm2/s) in the 20 - 80 keV energy range.

The main part of the INTEGRAL follow-up observation was centered on
the candidate optical counterpart SSS17a (RA=13:09:48.089
Dec=-23:22:53.35; GCN 21529
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 ).  This observation spanned from
2017-08-18 12:45:10 to 2017-08-23 04:07:47 (starting about 24 hours
after the LIGO/Virgo event), with a maximum on-source time of about
330 ks (depending on the instrument).

SSS17a was in IBIS and SPI FoV in each of the dithered single pointing
that make up an INTEGRAL observations; whilst it was in the JEM-X FoV
only a fraction of the time.

We investigated the complete observation mosaics of ISGRI, SPI, and
JEM-X data. INTEGRAL provides the most stringent constraint on any
possible emission associated with SSS17a above 80 keV. We do not
detect the source in any energy ranges of any of the INTEGRAL
instruments, and set the following 3-sigma upper bounds for an average
flux of a source at the position of SSS17a:

JEM-X:

3-10 keV:       1.2 mCrab (1.9e-11 erg/cm2/s )
10-25 keV:      0.64 mCrab (7e-12 erg/cm2/s )

ISGRI:

20-80 keV:      2.6 mCrab (3.8e-11 erg/cm2/s)
80-300 keV:     6.2 mCrab (7.1e-11 erg/cm2/s)
300-500 keV:    291.6 mCrab (1e-9 erg/cm2/s)

SPI:

20 - 80 keV:    7.2 mCrab (1.1e-10 erg/cm2/s)
80 - 300 keV:   24 mCrab (2.8e-10 erg/cm2/s)
300 - 500 keV:  175 mCrab (6.1e-10 erg/cm2/s)
500 - 1000 keV: 770 mCrab (3.1e-9 erg/cm2/s)
1 MeV - 2 MeV:  1.0 Crab (3.3e-9 erg/cm2/s)

We have also searched for isolated line-like features in ISGRI and SPI
data, and preliminary analysis did not identify any such
features. Further analysis is ongoing.

IBIS, SPI, and JEM-X observed more than 97% of the of LIGO
localization in the combined observation mosaic.  We searched
IBIS/ISGRI and JEM-X data for any new point source in the whole 90%
LIGO/Virgo localization region, and did not find any. The sensitivity
depends on the location, with the best value close to that computed
for SSS17a.

Continuous observation provided by INTEGRAL allows us to perform an
exhaustive search for any short (magnetar-like) or long bursts from
SSS17a. We build IBIS/ISGRI light-curves in 2 energy ranges: 20-80 keV,
80-300 keV, on 100 ms, 1 s, 10 s, and 100 s time scales. The
lightcurves span from 2017-08-18T12:45:10 to 2017-08-23T04:07:47 with
a coverage fraction of 80%. We did not find any deviations from the
background, and set a 3-sigma upper limit on any possible 1-s long
burst flux of 1.0 Crab (1.4e-8 erg/cm2/s) in 20-80 keV, and 6.8 Crab
(7.8e-8 erg/cm2/s) in 80-300 keV.

We also inspected the JEM-X (3-25 keV) light curves at 10 s time
scale, and did not find any significant fluctuations apart from
sporadic particle contaminations). The corresponding upper limit in
3-25 keV is 0.4 Crab (1.3e-8 erg/cm2/s).

Analysis of the PICsIT spectral-timing data with 100 s time resolution
in four energy bands spanning 208-2600 keV did not reveal any
significant variability associated with SSS17a during revolutions 1852
and 1853.

During these observation INTEGRAL/IBAS system identified two weak
triggers (at 2017-08-22 21:05:59 and 2017-08-22 05:48:21). The
localization of these events is not compatible with SSS17a. We
consider these events to be noise associated with moderate solar
activity.

Unfortunately, the optical camera on-board INTEGRAL, OMC, was unable to
disentangle SSS17a from the host galaxy NGC4993.

We acknowledge the exceptionally efficient support by the teams at
ESAC and ESOC for the scheduling of this follow-up observation.

K. Bannister (ATNF), R. Shannon (ATNF/ICRAR/Curtin University), A.
Hotan (ATNF), C. James (ICRAR/Curtin University/CAASTRO), S. Oslowski
(Swinburne University), W. Farah (Swinburne University).

We observed the 90% containment region of the Bayestar map (Singer et
al. LVC GCN 21513
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 ) with 7 antennas of the The Australian Square
Kilometer Array Pathfinder (ASKAP). We recorded fast autocorrelation
data with 336 x 1 MHz channels and a time sampling of 1.26 ms centered
at 1320 MHz (see [1] for observing details). We used flys-eye
observing mode, with some parts of the field covered by 2 antennas and
some by 1 antenna.

We had 3 observing runs with start times (UTC) and durations as shown below:

2017-08-18 04:05 3.6 hrs
2017-08-18 08:57 4.1 hrs
2017-08-19 02:08 11.0 hrs

We searched out to a dispersion measure of 2000 pc/cm3 and width
boxcar widths from 1 to 32 samples.

We found no fast radio bursts above a threshold of approximately 40 Jy/sqrt(ms).

We thank the CSIRO staff for supporting these observations.


[1] Bannister et al. 2017, ApJL, 841, 12


-- 
Keith Bannister

C. Lynch (University of Sydney), T. Murphy (University of Sydney),
D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney)
on behalf of the VAST collaboration.

Following Bannister et. al. (LVC GCN 21559
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 ) and Kaplan et al. (LVC GCN
21574
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 ),
we observed a second epoch of NGC 4993 with the Australia Telescope Compact
Array at 8.5 and 10.5 GHz. Observations started at 2017-08-20 23:31:02.9 UT
and ended at 2017-08-21 11:20:00 UT with approximately 13 minutes of
on-source
time.

We fit and subtracted a point-source at the optical position of NGC 4993
(13:09:47.71, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source
Catalog).
From this we set a 3-sigma upper limit of 135 uJy and 99 uJy on radio
emission
from SSS17a at 8.5 and 10.5 GHz respectively.

Subsequent epochs are planned.

Thank you to CSIRO staff for supporting these observations.

Po-Chieh Yu (NCU), C.-C. Ngeow (NCU), W.-H. Ip (NCU) on behalf of the
GROWTH (Global Relay of Observatories Watching Transients Happen
collaboration)


Ogando et al. (2008) measured velocity dispersion and Lick indices for the
candidate host galaxy NGC 4993 using long-slit spectra obtained with the
1.52m ESO telescope. From their measurements of the central velocity
dispersion (163 km/s), we obtained the central black holes mass of
log(Mbh/Msun) ~ 7.7 using the relation given by Ferrarese & Merritt (2000).
We decomposed Pan-STARRS stacked r-band image of the galaxy using Galfit
(Peng et al. 2010). Our initial analysis obtained that the Sersic index n
=1.27. Using the Mbh-n relation (Savorgnan et al. 2013) gives a similar
estimation of the black hole mass log(Mbh/Msun) = 7.25. We also obtained the
effective radius Re = 2.8 kpc; the OT is located at ~2.2 kpc (0.78 Re) from
the nucleus.


We estimated the bolometric luminosity L_bol = 8.96e40 erg/s by adopting
Lx=5.6e39 erg/s (Evans et al. LVC GCN 21612
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 ) and using bolometric
correction Lbol/Lx = 16 for low-luminosity AGNs (LLAGNs; Ho 2008). We
obtained the Eddington luminosity L_Edd = 1.26e45.7 erg/s by using the Mbh
= 10e7.7 Msun given in this circular. This gives the Eddington ratio
L_bol/L_Edd = 7e(-5.7), which is similar to ratios of other LLAGNs (Ho
2008).


The galaxy has 18 companions, and it is considered to be located in medium
density regions (4 < N < 22) (Ogando et al. 2008). The galaxy mass
estimated by the effective radius and the central velocity dispersion
(Burstein et al.1997) is log(M*/Msun)=10.64, which is similar to the mean
value of the S0 sample of Ogando et al. (2008).


Our residual image of subtracting an IRAF elliptical model from the HST
archival ACS image  (F606W) shows clearly complicated dust lanes that are
extended from the nucleus to outer kpc regions, as mentioned in Foley et
al. (LVC GCN 21536
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 ). NGC 4993 could be a radio AGN (LVC GCN 21537
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 , 21548
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 ,
21645
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 ). HST images show that some radio galaxies have optical jets (M87,
3C15, 3C78, 3C264). But no optical jets can be seen in our residual map of
NGC 4993.


In summary, the properties of the candidate host galaxy NGC 4993 seem to be
similar to normal early type galaxies, as indicated by Sadler et al. (LVC
GCN 21645
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 ).

A. Corsi (TTU), M.M. Kasliwal (Caltech), D. Frail (NRAO), and N.T. Palliyaguru (TTU) report 
on behalf of a larger collaboration:

We observed the field of SSS17a/DLT17ck (e.g., Coulter et al. LVC GCN 21529
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 ; Allam et al. LVC GCN 21530
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 ; 
Yang et al. LVC GCN 21531
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 ), the possible counterpart of G298048 (LVC, LVC GCN 21505
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 ) in NGC 4993, with the 
Karl G. Jansky VLA. The observation lasted 1 hr, centered on 2017-Aug-22.88 UT, and was conducted in C-band 
(approximate central frequency of 6 GHz). Our preliminary analysis does not show evidence for significant 
emission at the location of the optical candidate SSS17a/DLT17ck, down to a 3-sigma limit of about 20 uJy. 
Further observations are planned.

P. D'Avanzo, A. Melandri, S. Covino (INAF-OAB), M. G. Bernardini (LUPM/INAF-OAB), M. Branchesi (GSSI), 
S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC), M. Della Valle (INAF-OAC), Y. Z. Fan (PMO, Nanjing),
G. Ghirlanda, G. Ghisellini (INAF-OAB), L. Nava (INAF-OATs/INAF-OAB), E. Palazzi (INAF-IAFS Bo), 
A. Pescalli (Univ. Insubria/INAF-OAB), T. Piran (HUJI), S. Piranomonte (INAF-OAR), 
O. S. Salafia (Univ. Bicocca/INAF-OAB), R. Salvaterra (INAF-IASF Mi), G. Stratta (Urbino University/INFN Firenze), 
G. Tagliaferri (INAF-OAB), E. Troja (NASA-GSFC), S. D. Vergani (Obs. Paris/CNRS/INAF-OAB), Z. P. Zhin (PMO, Nanjing), 

and

G. Greco (Urbino University/INFN Firenze), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), 
S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC),  E. Cappellaro (INAF-OAPD),  
F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), 
E. Pian (SNS-Pisa), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), 
S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report:


We observed the transient SSS17a in NGC 4993 reported by Coulter et al. (LVC GCN 21529
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 ) with the ESO/VLT UT1 
equipped with the FORS2 camera. Imaging observations were carried out on 2017 Aug 21 starting at 23:23:10 UT 
during twilight (about 4.5 days after the LIGO/Virgo event; LVC GCNs 21509
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 ) with the B, V, R, I and z filters. 
The source is detected in all bands, showing a red color. From preliminary photometry (likely contaminated by the host 
galaxy light) we measure the following AB magnitudes:

R = 19.4 +/- 0.2
z = 18.5 +/- 0.2 

calibrated against the USNOB1 and PAN-STARRS catalogues. 


We acknowledge excellent support from the from the ESO observing staff in Paranal, in particular Jesus M. Corral-Santana 
and Stephane Brillant.

K. P. Mooley (Hintze Fellow, Oxford) and G. Hallinan (Caltech) report on 
behalf of the JAGWAR team

We have initiated deep S band (2-4 GHz) observations of the potential 
host galaxies of the GW event G29048 from the CLU list (Cook et al. 
2017, LVC GCN 21535
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 ). The pointings, observed as part of the Jansky 
Array mapping of GW bursts as Afterglows in Radio (JAGWAR) program, have 
RMS noise between 10-20 uJy. The first observing epoch of NGC 4993 on 
2017 Aug 20.93 shows no radio source at the location of SSS17a (Coulter 
et al. 2017, LVC GCN 21529
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 ), with a 3sigma upper limit of ~40 uJy. We 
will report any radio transients found through the LVC GCN system.

We thank the VLA staff for scheduling these observations.

R. Margutti, W. Fong (Northwestern), E. Berger (Harvard), R. Chornock (Ohio
University), P. Cowperthwaite, K. D. Alexander (Harvard)

We observed the field of the EM counterpart to the LVC trigger G298048 with
the Chandra X-ray Observatory (CXO) starting on 2017-08-19T17:10:09UT  (PI
Fong).
We do not find evidence for significant X-ray emission at the location of
the optical transient (RA= 13:09:48.08, Dec= -23:22:53.2,  Coulter et al.
LVC GCN 21529
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 ; Allam et al., LVC GCN 21530
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 ; Sheng Yang et al., LVC GCN
21531
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 ; Chambers et al. LVC GCN 21553
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 ).

An extended X-ray source is clearly detected at:
RA= 13:09:47.7
dec= -23:23:02.0

This position is consistent with the radio source that we identified in
Alexander et al. (LVC GCN 21589
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 ) and it is centered on the host-galaxy
optical position. Based on preliminary analysis, we estimate a flux ~1e-14
erg/s/cm2 in the 0.3-10 keV band.

The CXO X-ray source lies outside the 90% containment, but within the
3-sigma containment, of the localization region of the Swift-XRT source
(Evans et al., LVC GCN 21612
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 ). The flux inferred by Evans et al., Fx=2.6
(+1.1, -0.9) e-14 erg/cm^2/s is also consistent with our results. We thus
suggest that the X-ray source identified by Swift-XRT is most likely
emission from the host galaxy.

We thank Belinda Wilkes and the entire Chandra team for their great support
with these observations.

E. M. Sadler (University of Sydney), J. R. Allison (University of Sydney), D. L. Kaplan (UWM), T. Murphy (University of Sydney) on behalf of the VAST collaboration.

The global properties of the candidate host galaxy NGC 4993 appear entirely consistent with those of a normal early-type galaxy, with a negligible level of ongoing star formation. 

An archival optical spectrum from the 6dF Galaxy Survey (6dFGS; Jones et al. 2009) is dominated by the light of an old stellar population along with weak H-alpha and [NII] emission lines. The relatively high [NII]/H-alpha emission-line ratio is suggestive of a low-ionisation AGN rather than star formation. The galaxy is devoid of any large neutral gas reservoir, with an upper limit to the neutral hydrogen mass of M_HI < 2e9 Msun (HIPASS; Meyer et al. 2004).

The 6dFGS fibre (6 arcsecond diameter) only covers the central region of the galaxy, and excludes the location of the putative optical counterpart, so it is still possible that star formation could be occurring outside the region covered by the 6dFGS spectrum. To check this, we looked at several photometric indicators of the current rate of massive star formation across the galaxy as a whole. 

We caution that all the values derived here should be considered as upper limits because of the possibility of contamination from a central AGN. From GALEX photometry (S_NUV ~ 1.08e-4 Jy) we obtain a near UV luminosity of L_NUV ~ 1.9e19 W/Hz. Using the relations from A. Hopkins (PhD thesis) and Cowie et al. (1997) gives an estimated NUV-derived star formation rate of SFR(NUV) ~ 0.003 Msun/yr for massive stars with M > 5 Msun. This low star formation rate is consistent with the global upper limit from far infrared photometry.  NGC 4993 is undetected by IRAS, so we adopt a conservative upper limit of 0.25 Jy for the FIR flux density at 60 microns. This gives a 60 micron luminosity L_FIR < 4.3e22 W/Hz. From Condon et al. (1992), this translates to a star formation rate (for stars more massive than 5 Msun) of SFR(FIR) < 0.08 Msun/yr. 

The existence of a low-luminosity radio-emitting active galactic nucleus in this galaxy is not surprising. The bivariate radio luminosity function of Mauch & Sadler (2007) implies that approximately 10% of galaxies of similar stellar mass to NGC 4993 host a radio AGN at least as strong as the central radio source reported for NGC 4993 (LVC GCNs 21537
Loading...
 
 , 21548
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 , and others), so the presence of this source is not unusual. The nuclear dust lanes evident in the HST ACS images (Foley et al. LVC GCN 21536
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 ) are similar to those seen in many other early-type galaxies, and may be the product of a minor merger than occurred as long as several Gyr ago.  

In summary, there is persuasive evidence that the current rate of massive-star formation in NGC 4993 is very low. We therefore speculate that the massive-star progenitors of the binary neutron-star system are likely to have formed and exploded several Gyr ago, implying a long in-spiral time for the neutron-star pair that produced the GW event.

A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), 
M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration:

We continue observation of  the possible counterpart SSS17a/DLT17ck 
(Coulter et al. GCN 21529
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 ;  Yang et al., GCN 21531
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 ) of LIGO/Virgo 
trigger G298048 (GCNs 21509
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 , 21513
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 )  with RC-1000 telescope of 
CHILESCOPE observatory. The observations carried out in clear filter 
starting on Aug. 21  (UT) 23:32:09.

Preliminary Photometry of the transient SSS17a/DLT17ck is following

Date       UT start  MJD          Filter  OT   Err UpLim (3 sigma)

2017-08-21 23:32:09  57987.00386  CR      18.8 0.2 22.2

The photometry is based on several nearby USNO-B1.0 stars (R2). The 
photometry  is still preliminary and required  careful estimation of 
NGC4339 influence.

We are grateful for the team of remote controlled CHILESCOPE observatory 
(www.chilescope.com) for observations.

S. Nakahira (RIKEN), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama,
Y. Yamada, A. Tezuka, S. Matsukawa (AGU), K. Yamaoka (Nagoya U),
I. Takahashi (IPMU), Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger time
of G298048 (The LIGO Scientific Collaboration and the Virgo Collaboration,
GCN Circ. 21509
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 ).  No CGBM on-board trigger occurred at the time
of the event.  Based on the updated LVC localization sky map
(preliminary-LALInference.fits.gz), none of the probability area was in the
field-of-view of the CGBM/HXM.  However, 99% of the summed probability was
inside the field-of-view of the CGBM/SGM.  The CGBM/SGM boresight position
(R.A., Dec. = 223.8 deg, 43.4 deg) was 73 deg off-axis from the maximum LVC
probability location (The LIGO Scientific Collaboration and the Virgo Collaboration,
GCN Circ. 21527
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 ).

Based on the analysis of the light curve data with 0.125 sec time resolution
from -60 sec to 60 sec from the trigger time, we found no significant excess
around the trigger time in either the HXM (7-3000 keV) or the SGM (40 keV -28 MeV)
data.  The incident angle of SGM to the position of SSS17a (Coulter et al.,
GCN Circ. 21529
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 ) was 71 deg.  Assuming the association of GRB 170817A
(Connaughton et al., GCN Circ. 21506
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 ) and SSS17a, we estimated the upper
limit of the SGM.  The 7-sigma upper limit of SGM using alpha=-0.9 and Epeak=130 keV
(Goldstein et al., GCN Circ. 21528
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 ) is 5.5e-7 erg/cm2/s in the 10-1000 keV band
at 1 s exposure assuming no shielding by ISS structures.  This estimated upper
limit is at the similar level to the reported peak flux, 7.3e-7 erg/cm2/s, of
GRB 170817A by Fermi-GBM.  We further noticed that the position of SSS17a
was covered by the large structure of ISS at the time of the trigger.  Because
of this, the SGM sensitivity should be worse than what we reported above.
Therefore, it is consistent that no signal of GRB 170817A is seen by the SGM data.

The CALET Calorimeter (CAL) was operating in the high energy trigger mode at the
trigger time of G298048.  However, no LVC high probability region was included
in the CAL's field of view at the time of the trigger.

D. Dobie (University of Sydney), A. Hotan (CSIRO), K. Bannister (CSIRO),
T. Murphy (University of Sydney), D. Kaplan (UWM), C. Lynch (University of
Sydney),
on behalf of the ASKAP/VAST collaboration.

We have observed the LIGO/Virgo localisation region (LVC GCN 21527
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 )
with the Australian Square Kilometre Array Pathfinder (ASKAP) at a
central frequency of 1.345 GHz with a bandwidth of 192 MHz. Observations
started at 2017-08-19 05:34 UT and ended at 2017-08-19 07:58 UT.

We do not detect any emission at the position of the possible optical
counterpart SSS17a (Coulter et al. LVC GCN 21529
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 ), or its candidate
host galaxy NGC 4993. The upper limit for NGC 4993 is consistent with
a spectral index of -0.7 found by fitting the measured results from
the ATCA (Bannister et al. LVC GCN 21559
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 ) between 8.5 and 21.2 GHz.

Further analysis of our observations is ongoing.

Thank you to CSIRO staff for supporting these observations.

R. Chornock (Ohio University) and E. Berger (Harvard) report on behalf of a 
larger collaboration:

We have been obtaining a sequence of near-infrared spectroscopy (range 1-1.8 
microns) of the optical counterpart (SSS17a: Coulter et al., GCN 21529
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 ; Allam et 
al., GCN 21530
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 ) of LIGO/Virgo G298048 (GCNs 21509
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 , 21513
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 ) using FLAMINGOS2 on 
Gemini-South (PI: Chornock).

Our initial spectra, taken on 20170819 at 00:45 UT (~1.5 days after the 
LIGO/Virgo event) have a smooth blue continuum.  Data taken the following night 
show a few broad, low-amplitude features starting to develop.  An initial 
reduction of data taken on 20170821 at 23:40 UT (~4.5 days after the LIGO/Virgo 
event) shows that these features (including a possible spectral peak near 1.05 
microns) have strengthened.  Analysis is ongoing and further observations are 
planned to constrain the potential presence of lanthanide opacities in the 
near-infrared.

We thank the Gemini staff, particularly Hwihyun Kim, Gonzalo Diaz, Pablo Candia, 
and Laura Ferrarese for their support of these operations.

D. Kaplan (UWM), M. Sokolowski (Curtin University), R. Wayth (Curtin University), T. Murphy (University of Sydney), D. Dobie (University of Sydney), C. Lynch (University of Sydney), and K. Bannister (CSIRO) on behalf of the MWA collaboration.

We have observed a 20 x 20 deg field-of-view centered on the  LIGO/Virgo G298048 localization region  (LVC GCN #21513
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 ) with the Murchison Widefield Array.  Observations occurred on 2017-08-18, 2017-08-19, 2017-08-20, 2017-08-21, and 2017-08-22, all from roughly 07:00 UT to 09:30 UT, at a central frequency of 185 MHz.  Note that the array is in the process of being reconfigured, so only 5/16 of the tiles are operational.  Analysis of this data is underway, and subsequent epochs are planned.

We thank the MWA Operations team for supporting these observations.

A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration:

We analyzed the Karl G. Jansky VLA observation of the field of the possible optical counterpart SSS17a (Coulter et al. LVC GCN 21529
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 ) that started on 2017-Aug-19 22:01:48 UT (Corsi et al. LVC GCN 21613
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 ). At a central frequency of ~15 GHz, our preliminary analysis does not show evidence for significant emission at the location of the optical candidate (RA= 13:09:48.089, Dec= -23:22:53.35, Coulter et al. LVC GCN 21529
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 ) down to a 3-sigma limit of ~16 uJy. The host galaxy (RA = 13:09:47.704, Dec =-23:23:02.45; Alexander et al. LVC GCN 21589
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 ) is clearly detected (flux level of ~0.25 mJy at 15 GHz).

A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), 
M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration:

We observed  the possible counterpart SSS17a/DLT17ck (Coulter et al. 
GCN 21529
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 ;  Yang et al., GCN 21531
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 ) of LIGO/Virgo trigger G298048 (LVC 
GCNs 21509
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 , 21513
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 )  with RC-1000 telescope of CHILESCOPE observatory. 
The observations carried out in clear filter in two epochs, on Aug. 19 
and Aug.20.

Photometry of the transient SSS17a/DLT17ck is following

Date       UT start  Filter    OT   Err UpLim (3 sigma)


2017-08-19 23:30:33   CR       16.7 0.2 21.9
2017-08-20 23:21:09   CR       18.5 0.2 22.0

The photometry is based on several nearby USNO-B1.0 stars (R2). The 
photometry  is still preliminary and required  careful estimation of 
NGC4339 influence. Nevertheless it is evident the source is fading 
significantly which is confirmed by many observations (e.g. Im et al., 
GCN 21632
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  and references in the GCN 21632
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 ).

We are grateful for the team of remote controlled CHILESCOPE observatory 
(www.chilescope.com) for observations.

Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon(Univ La Serena)

We report a spectrum observation of SSS17a in CASLEO Observatory, Argentina.

Telescope: Jorge Sahade
Reflector Ritchey Chretien
Primary mirror diameter: 2153 m
Geographic coordinates: 
Lon = W 69 18 23.16
Lat = -31 47 14.46

Reosc Spectrograph
Diffraction grating of 300 lin/mm (blaze at 500 nm)
Simple dispersion configuration
Slit width of 350 microns = 1 arcsec
Spectral Resolution: 13.5 Angstrom
Slit Orientation: E-W

Observations performed on 08/19/2017 (the night of 18)
starting at approximately  00:15 UTC
finishing at approximately 01:30 UTC

Performed 3 integrations of 1200 seconds
Atmospheric conditions: clear sky; seeing approx. >2 arcsec

Martin Beroiz on behalf of TOROS Collaboration.

K. C. Chambers (IfA), M. E. Huber (IfA),K. W. Smith (QUB),
S. J. Smartt, (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen
(MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare
(QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder
(IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters,
R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB)

We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck
in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553
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  for
more details of filters, photometry, methods etc).

Our reference stack and calibrations provide rapid reliable photometry
with the host removed and we will continue to post updates while it is
visible from Hawaii.  A series of short exposures to avoid sky
saturation in twilight in each of i, z, and y provide average nightly
magnitudes (AB) as follows. 

Pan-STARRS is observing at lower altitude than it has ever done, Poor
conditions and airmass>3 hampered the fourth night of observing (57986
= 2017-08-21 UT).  The difference images showed faint flux in z band,
but no detection in i and y. The forced photometry in the z-band at
the position of the transient is reported. The quick estimates for i
and y need to be verified.

MJD             i       err 
57983.23	17.24	0.06
57984.24	17.91	0.05
57985.24	18.47	0.08
57986.24        <18.5   limit only    

MJD             z       err 
57983.23	17.26	0.06
57984.24	17.80	0.05
57985.24	18.31	0.06
57986.24        18.27   0.33 

MJD             y       err 
57983.23	17.38	0.10
57984.24	17.59	0.07
57985.24	18.08	0.07
57986.23        <18.0   limit only

M. Im, C. Choi, J. Kim, Lim, G. H. M. Lee (SNU), S.-L. Kim, C.-U. Lee
(KASI) on behalf of the KU collaboration


We continued to monitor the strong optical counterpart candidate of
LIGO/Virgo G298048 (GCNs 210505
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 , 21509
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 , 21513
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 ), SSS17a/DLT17ck(Coutler et
al. GCN 21529
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 ; Allam et al. GCN 21530
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 ; Yang et al. GCN 21531
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 ; Arcavi et al.
GCN 21538
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 ; also see notes below for a list of optical/NIR observation
reports). The observation was carried out using three KMTNet 1.6m
telescopes and other small telescopes (Im et al. GCNs 21563
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 , 21566
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 , 21597
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 )
at three sites , the Siding Spring Observatory (SSO), the South African
Astronomical Observatory (SAAO), and the Cerro-Tololo Inter-American
Observatory (CTIO). We imaged the object with B,V,R,I,i,z, filters and
medium-band images at 825, 875, 925, 975 nm.

We confirm that the object is fading in optical and its continuum shape has
been becoming redder as time goes on (e.g., Cenko et al. GCN 21572
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 ; Lyman
et al. GCN 21582
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 ; Wiseman et al. GCN 21584
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 ; Chambers et al. GCN 21590
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 ;
Malesani et al. GCN 21590
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 ; Chen et al. GCN 21608
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 ). A part of the data from
several sites are presented below.

UT V R I Site

08-18.72 17.8(0.1) 17.4(0.1) 17.3(0.1) SAAO

08-18.99 18.3(0.1) 17.6(0.1) 17.4(0.1) CTIO

08-19.72 19.4(0.1) 18.3(0.1) 17.9(0.1) SAAO

08-19.98 19.8(0.1) 18.4(0.1) 18.2(0.1) CTIO

The observations and further analysis of the data are ongoing.

Notes: It is remarkable that more than 40 optical/NIR follow-up
imaging/spectroscopic observations of the optical counterpart candidates
have been reported in three days since the first discovery report of the
optical counterpart. For reference, we list them here (let me know if I am
missing any). They are, Coutler et al. (GCN 21529
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 , 21567
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 ), Allam et al.
(GCN 21530
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 ), Yang et al. (GCNs 21531
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 , 21579
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 ), Melandri et al. (GCN 21532
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 ,
21596
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 ), Arcavi et al. (GCNs 21538
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 , 21565
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 , 21581
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 ), Nicholl et al. (GCN
21541
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 , 21580
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 , 21585
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 ), Tanvir et al. (GCN 21544
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 ), Lipunov et al. (GCNs
21546
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 , 21570
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 , 21587
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 ), Drout et al. (GCN 21547
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 ), Evans et al. (GCN 21550
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 ),
Simon et al. (GCN 21551
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 ), Singer et al. (GCN 21552
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 ), Chambers et al. (GCN
21553
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 , 21590
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 , 21617
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 ), Wolf et al. (GCN 21560
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 ), Yoshida et al. (GCN 21561
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 ,
21586
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 ), Im et al. (GCNs 21563
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 , 21566
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 , 21597
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 ), Cenko et al. (GCN 21572
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 ),
Lyman et al. (GCN 21582
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 ), Kilpatrick et al. (GCN 21583
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 ), Wiseman et al.
(GCN 21584
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 ), Malesani et al. (GCN 21591
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 ), D���Elia et al. (GCN 21592
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 ),
Wiersema et al. (GCN 21594
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 ), Tominaga et al. (GCN 21595
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 ), Valenti et al.
(GCN 21606
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 ), Chen et al. (GCN 21608
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 ), Pozanenko et al. (GCN 21618
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 ), Nakaoka
et al. (GCN 21623
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 ), Castro-Tirado et al. (GCN 21624
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 ), Coward et al. (GCN
21627
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 ).

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. Dornic
(CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T. Pradier (IPHC/Universite
de Strasbourg) report on behalf of the ANTARES Collaboration:

The refined location of the LIGO/Virgo G298048 event (90% confidence level contour
Bayestar-HLV) falls outside the optimum field of view of ANTARES (as defined with
upward going events). GCN #21522
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  reported the results of the upward going neutrino search.
As a consequence, we have performed a dedicated analysis looking for down-going neutrino
candidates in the on-line ANTARES data stream. Cuts on the quality of the track reconstruction
and an energy proxy have been used to reduce the false alarm rate in such a way that one
event matching in time (+/- 500 s) and direction (90% C.L contour) with G298048 would
result in a 3-sigma excess.

The ANTARES visibility, for down-going events, at the time of the alert together with
the 90% contour of the probability map are shown in:
https://www.cppm.in2p3.fr/~dornic/events/G298048/gw190817_visi_down.png <https://www.cppm.in2p3.fr/~dornic/events/G298048/gw190817_visi_down.png> (gwantares/GW@ANT31).

No down-going muon neutrino candidate events were recorded by ANTARES within the 90% C.L.
contour and  during a +/- 500 s time-window centered on the G298048 event time. An extended
search during +/- 1 hour yields no coincidence.

An estimate of the upper limit on the associated neutrino fluence will be sent in a subsequent
circular.

ANTARES, being installed in the Mediterranean Deep Sea, is the largest neutrino detector in the
Northern Hemisphere. It is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy
range. At 10 TeV, the median angular resolution for muon neutrinos is below 0.5 degrees.

C. Lynch (University of Sydney), T. Murphy (University of Sydney),
D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney)
on behalf of the VAST collaboration.

We report a correction to the radio upper limits announced in GCN 21628
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 .
All values are the 1-sigma limits at the location of each source, not the
3-sigma
limits as stated.  We apologise for the error.

C. Lynch (University of Sydney), T. Murphy (University of Sydney),
D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney)
on behalf of the VAST collaboration.

We have observed 54 galaxies in the localisation volume of G298048 as
listed by
Cook et al. (LVC GCN 21519
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 ) with the Australia Telescope Compact Array at
8.5 GHz (Bannister et al. LVC GCN 21537
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 ). The observations were taken in the
EW352 configuration, with approximately 1-2 minutes on each source between
2017-08-18 01:00 UT and 2017-08-18 09:14:15 UT.

We detected 8.5 GHz radio emission from 5 galaxies, as listed below:

Galaxy                  3-sigma flux density
UGCA 331            0.33 mJy
NGC 4993            0.66 mJy
NGC 4968            16.1 mJy
IC 4197                 2.7 mJy
ESO 508- G 033   3.7 mJy

The rest of the sources in the list were non-detections. We list 3-sigma
upper limits on the 8.5 GHz radio emission below:

Galaxy                                                       3-sigma flux
density limit
IC 3825                                                      102.8 uJy
ABELL 1631:[CZ2003]B0295[024]            47.1 uJy
GALEXASC J125157.02-160617.8           43.7 uJy
MCG -02-33-036                                        24.9 uJy
2MASX J12525109-1529300                    33.2 uJy
GALEXASC J125301.39-151007.7           36.9 uJy
WINGS J125412.84-153523.6                   25.9 uJy
6dF J1254495-160308                               36.2 uJy
GALEXASC J125520.46-170546.9            33.6 uJy
HIPASS J1255-15                                       36.5 uJy
ESO 575- G 029                                         46.8 uJy
MCG -03-33-023                                        198.8 uJy
WINGS J125701.38-172325.2                   213.4 uJy
NGC 4830                                                  60.0 uJy
GALEXASC J125811.97-210246.3            22.6 uJy
GALEXASC J130415.26-225251.3            21.2 uJy
ESO 575- G 053                                         50.4 uJy
6dF J1305235-233121                               18.2 uJy
GALEXASC J130525.30-233008.8            12.8 uJy
2MASX J13061939-2258491                      77.5 uJy
ESO 508- G 003                                          60.3 uJy
ESO 575- G 055                                          85.7 uJy
ESO 508- G 004                                          66.2 uJy
UGCA 325                                                   35.0 uJy
GALEXASC J130707.37-240634.4             35.0 uJy
NGC 4970                                                   48.5 uJy
ABELL 1664_11:[PSE2006] 2506               54.7 uJy
ESO 508- G 010                                         39.2 uJy
UGCA 327                                                  39.8 uJy
USGC S204                                                44.5 uJy
HDCE 0763                                                39.2 uJy
ESO 508                                                     62.8 uJy
ESO 508- G 014                                         56.0 uJy
2MFGC 10461                                            44.3 uJy
6dF J1309177-242256                               24.6 uJy
GALEXASC J130918.58-242304.8            25.6 uJy
UGCA 328                                                  23.1 uJy
ESO 576- G 003                                         49.4 uJy
[TSK2008] 0073                                          32.2 uJy
GALEXASC J131426.62-271242.6            53.4 uJy
[TSK2008] 0052                                          56.6 uJy
ESO 508- G 035                                         70.5 uJy

We have not yet been able to make reliable measurements for the following 7
sources, so they are excluded from the above lists:

2MASX J12505229-1454238
2MASX J12573271-1942006
2MASX J13073768-2356181
GALEXASC J125259.36-152150.9
IC 4180
2MFGC 10484
ESO 508- G 019

We did not observe GALEXASC J120652.88-040236.6.

Further observations are underway. Thank you to CSIRO staff for supporting
these observations.

D. Coward (UWA), E. Howell (UWA), R. Laugier (OCA), A. Klotz (UNS-CNRS-OCA), M. Boer  (UNS-CNRS-OCA),  I. Andreoni (Swinburne), J. Cooke (Swinburne), D. Macpherson (UWA), J. Moore (UWA) and A. Burrell (UWA) report on behalf of OzGrav and TZAC  (see acknowledgements below):

We report Zadko Telescope imaging of the transient SSS17a/DLT17ck in NGC4339 started at 2017-08-20 10:59 UT. In a preliminary analysis using background subtraction of the host galaxy NGC4339 through rotational masking, a photometric calibration using the star NOMAD-10666-0296310 (R=17.35) yields a magnitude of the optical transient R=20.05 +/- 0.15.

Acknowledgments:
The Zadko Telescope is operated by the University of Western Australia (UWA), and was made possible by a philanthropic donation by James Zadko to UWA. The facility receives support from the ARC Centre of Excellence "OzGrav" for gravitational wave follow-up and discovery. Key personnel include D.Coward (Director-UWA), E. Howell (UWA), J. Moore (UWA), A. Burrel (UWA), A. Greensky, J. Kennewell with collaborators I. Andreoni and J. Cooke (Swinburne).

This observation report was done in partnership with the LIGO follow-up collaboration TZAC, which is supported by M. Boer, A. Klotz, R. Laugier, K. Noysena

F. A. Harrison, K. Forster, J. Garcia, B. W. Grefenstette, M. Heida, M. M.
Kasliwal, K. K. Madsen,  H. Miyasaka, S. Pike, V. Rana, Y. Xu (Caltech)

We obtained X-ray imaging of the optical counterpart of SSS17a (Coulter et
al.; GCN21529
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 ), the candidate optical counterpart of G298048 (LVC; GCN
21509
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 ) in the 3 ��� 79 keV band with NuSTAR.  Observations began at
2017-08-18T05:26:09 UT and ended at 2017-08-18T19:46:09, with a total
exposure of 24 ksec.  We did not detect any X-ray emission in a circular
50������ extraction region centered on the position of the optical counterpart,
with a 3-sigma threshold of 1.4 x 10-14 erg/cm^2/s in the 3-10 keV band,
assuming an X-ray spectrum with a photon power law index of -2.   No source
was detected in the 10-60 keV band, however additional analysis is ongoing
to place limits on possible line emission from nuclear decays. We note that
the NuSTAR hard X-ray band is not sensitive to X-ray emission from star
formation in the host galaxy, and there is no known AGN activity in this
source.

Further NuSTAR observations are planned.

D. Dobie (University of Sydney), A. Hotan (CSIRO), K. Bannister (CSIRO),
D. Kaplan (UWM), T. Murphy (University of Sydney), C. Lynch (University
of Sydney), on behalf of the ASKAP/VAST collaboration.

We are observing the LIGO localisation region (LVC GCN 21513
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 ) with the
Australian Square Kilometre Array Pathfinder (ASKAP) at a central
frequency of 1345 MHz with a bandwidth of 192 MHz. As the array is still
undergoing commissioning, we are using a nominal 12 (of 36) antennas,
although other site activities may cause that number to vary from one
observation to the next.

Our observing strategy consists of 3 pointings containing approximately
90% of the LIGO localisation region. Each pointing consists of a 5.5 x 5.5
degree square grid of 36 beams, though the exact number captured may
also vary. The first pointing is centered at

RA = 13:09:21.60
Dec = -25:00:00.00

and contains ~48% of the localisation region and the positions of 35
target galaxies (Cook et al. LVC GCN 21519
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 ) including NGC 4993, the
host of the possible optical counterpart SSS17a
(Coulter et al. LVC GCN 21529
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 ). Observations began at 2017-08-19
05:34:32 (UT) and are ongoing.

Processing and analysis of the first pointing is underway.

Thank you to CSIRO staff for supporting these observations.

A. J. Castro-Tirado (IAA-CSIC and ISA-UMA), J. C. Tello, Y. Hu, A. 
Gonz��lez-Rodr��guez, B.-B. Zhang, R. Cunniffe (IAA-CSIC), W. H. Lee, D. 
Hiriart (UNAM), S. Jeong and I. H. Park (SKKU), on behalf of a larger 
collaboration report:

In response to the LIGO/Virgo binary neutron star candidate G298048 on 
Aug 17 (GCNC 21509), we used the JGT 0.6m robotic telescope at the 
BOOTES-5 station at Observatorio Astron��mico Nacional de San Pedro M��rtir (M��xico) 
to image the 15 galaxies in the GLADE Catalogue (GCN 21516
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 ) starting on 
Aug 18.21 UT. The potential optical candidate (GCN 21529
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 ) was only 
imaged on Aug 19.21 UT, with the images quality being affected by the 
very high airmass and the twilight sky. The optical candidate (SSS17a) is 
only barely visible in the outskirts of the NGC 4993 galaxy. A more 
detailed analysis of the data is in progress.

We thank the staff of Observatorio Astron��mico Nacional in San Pedro M��rtir.

[GCN OPS NOTE(21aug17): Per author's request, (a) the SSS17a name was corrected
for a typo, (b) Lee's name was corrected, (c) OAN's name was corrected, and
(d) the second paragraph was added.]

T. Nakaoka, K. S. Kawabata, M. Kawabata, H. Nagashima, and 
Y. Utsumi (Hiroshima University) on behalf of J-GEM collaboration.

We performed H-band imaging of the possible counterpart of G298048,
SSS17a in NGC 4993 identified by Coulter et al. (LVC GCN  21529
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 ),
with HONIR on the 1.5-m Kanata telescope at Higashi-Hiroshima
Observatory, Japan.

Because of low-elevation observation (height~10 deg) during bright
twilight, the foreground sky level was still high and SSS17a was
considerably faint (~3 sigma) in our stacked image. We performed
a forced aperture photometry and estimated a preliminary magnitude
in AB system of

   H = 16.7 (2017 August 20.424-429 UT; MJD 57985.424-429)

The magnitude is calibrated against 2MASS field stars. Further 
analysis is in progress.

V.M.Lipunov,
Lomonosov Moscow State University, Sternberg Astronomical Institute

There are several very important arguments  for reality SSS17a as 
the kilonova  candidate  was published in LVC GCN. There are relativictic 
expansion  (see Nichol etal., LVC GCN 21585
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 ;) and big distance 
(delta ~ 3.9Mpc) 
between host galaxy explositions   ( D'Elia et al.,  LVC GCN 21592
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 ).

I point out that we can obtain minimal radial space velosity of the 
progenitor of the G298048:

      V_min = delta/T_Universe = 3.9 Mpc / 13.7 10^10 yrs  ~ 300 km/sec.

From other hand, because kick velosity realy is not more than 1000 km/s, 
we received typical age of the binary NS's as several billion years.

This is not contadict to Scenario Machine population synthesis of the 
NS+NS star merging rates evolution in Universe (Lipunov et al., 
1995, Evolution of  the Double Neutron Star Merging Rate and the 
Cosmological Origin of Gamma-Ray Burst Sources,1995,
Astrophysical Journal v.454, p.593; Lipunov & 
Pruzhinskaya; MNRAS, Vol. 440,  1193-1199, 2014.

From the other hand diference between NGC 4993 galaxy redshift and 
Kilonova ( D'Elia et al.,  LVC GCN 21592
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 ) may be explained by fast moving 
relativistic shell where some absobtion lines can be formed.

The NS+NS merging rate evolution from Lipunov et al., 1995 is available at
http://master.sai.msu.ru/static/images/green_function.jpg


This message can be citted.

Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon.


The following tables summarize the observations done to scan the probability region skymap for G298048.
The observations we carried over 3 nights, in Tolar Grande, Argentina with a Meade LX 200 GPS 16��� telescope.
Focal length: 4043mm; FOV : 15,3���x11,5��� and a SBIG STF 8300 camera.

2017-08-16:
Exposure time: 30s; Number of images: 123
NGC6397;  J2000   : 17h40m41.36s -53d40m25.26s
NGC6544;  J2000   : 18h07m20.001s -24d59m54.0798s

2017/08/17
Exposure time: 30s
NGC6397               : 17h40m41.36s -53d40m25.26s          Number of images: 80
NGC6544               : 18h07m20.001s -24d59m54.0798s    Number of images: 80
ESO320-007           : 11h35m45.276s -38d21m53.136s      Number of images: 15
ESO320-013           ; 11h37m19.884s -38d05m50.748s      Number of images: 15
ESO320-019           ; 11h44m45.924s -39d36m55.296s      Number of images: 10
ESO320-020           ; 11h46m00.048s -39d20m03.948s      Number of images: 10
ESO320-024           ; 11h49m26.004s -38d49m32.988s      Number of images: 10
ESO320-027           ; 11h50m24.756s -38d38m56.58s        Number of images: 10
ESO320-029           ; 11h52m42.132s -39d27m44.028s      Number of images: 12
ESO320-030           ; 11h53m11.76s -39d07m48.648s        Number of images: 12
ESO320-031           ; 11h54m06.84s -39d52m03.324s        Number of images: 10
ESO320-032           ; 11h54m39.024s -40d55m56.28s        Number of images: 10
PGC580951            ; 11h54m59.256s -40d55m26.976s      Number of images: 10
ESO320-035           ; 11h56m46.464s -38d11m32.928s      Number of images: 12
ESO175-002           :14h08m35.99s  -53d21m10.296s        Number of images: 20
ESO221-028           :14h09m02.20s -51d10m07.428s         Number of images: 22

2017/08/18 
Exposure time: 30s
NGC6397       	        : 17h40m41.36s -53d40m25.26s         Number of images: 82
NGC6544       	        : 18h07m20.001s -24d59m54.0798s   Number of images: 123
ESO175-002  	        :14h08m35.99s  -53d21m10.296s      Number of images: 40
ESO221-028           :14h09m02.20s -51d10m07.428s       Number of images: 40
PGC141857            :14h10m33.49s -52d19m01.416s       Number of images: 40
PGC448694            :14h10m37.02s -52d06m05.904s       Number of images: 40
ESO221-030           :14h10m41.12s -52d11m02.904s       Number of images: 33
PGC166335            :14h16m01.99s -53d42m59.4s           Number of images: 40
NGC4993	        :13h09m48,1s -23d23m53,4s             Number of images: 47 	


Martin Beroiz(UTRGV) on behalf of the TOROS Collaboration.

Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon

To scan the LVC uncertainty region for G298048 we pointed to 
14 targets covered in 6 pointings with telescope at La Serena, Chile, filter i, 2 sq deg FoV, 60s integration time.
The pointing centers are:

14:00:52.21,-48:23:31.8,2000.
14:12:08.50,-52:43:29.8,2000.
14:06:20.01,-51:04:30.7,2000.
14:05:12.66,-53:17:24.3,2000.
14:19:17.56,-55:22:04.4,2000.
14:18:58.06,-57:59:06.6,2000.

Targets covered:
PGC141857 : 14:10:33.6,-52:19:02,20"  
ESO221-030 : 14:10:41.1,-52:11:04,20" 
PGC448694  : 14:10:37.0,-52:06:06,20" 
PGC166335 : 14:16:02.0,-53:43:00,20"
PGC2800412 :  14:17:10.1,-55:32:39,20" 
ESO175-002 :  14:08:36.0,-53:21:10,20"
ESO221-028 : 14:09:02.2,-51:10:08,20"
ESO271-003 : 13:52:27.5,-43:52:53,20" 
PGC463082  : 14:03:29.3,-50:46:38,20"
ESO221-035 : 14:16:04.6,-52:36:31,20"
PGC141859 :  14:20:23.5,-55:04:08,20" 
PGC485499 :  14:03:11.9,-48:37:39,20"
ESO271-005 :  13:56:08.4,-45:39:34,20"
PGC166323 : 14:04:34.1,-52:41:50,20���

The observations started on 2017-08-17T01:37:00 UT and ended on 2017-08-17T04:42:00 UT.

Martin Beroiz (UTRGV) on behalf of the TOROS Collaboration.

A. Pozanenko (IKI), E. Mazaeva (IKI), A. Volnova (IKI),  P. Minaev 
(IKI), M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration:

We observed  the field of  LIGO/Virgo trigger G298048 (LVC GCNs 21509
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 , 
21513
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 ) and the error circle of GMB/Fermi short burst GRB 170817A 
(Connaughton et al., GCN 21506
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 ) with RC-1000 and ASA-500 telescopes of 
CHILESCOPE observatory located at W 70d 34m S20d 27m. The observations 
started on Aug 17 (UT) 23:17:16 in clear filter. The last image was 
recorded on 2017-08-18T00:59:48.

We cover central part of G298048 localization with typical limiting 
magnitude of 20m at 60 s exposure in each image. The covering map can be 
found in
http://grb.rssi.ru/GRB170817A/bayestar_RC1000%20coverage.png

The OT candidate found by Coulter et al. (LVC GCN 21529
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 ), the DLT17ck 
(Sheng Yang et al., GCN 21531
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 ) is out of the coverage in the first epoch 
of the observations.

We also cover northern part of GBM/Fermi  localization?  1-sigma 
containment, statistical only (Connaughton et al., GCN 21506
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 ). The 
coverage of the GBM localization is about 20%. Typical limiting 
magnitude of 17.5m at 60 s exposure in each image. The covering map can 
be found in
http://grb.rssi.ru/GRB170817A/GRB170817A_GBM_coverage_ASA500.png

The detailed investigation of the fields is underway.

We are grateful to the remote staff of the observatory for timely 
observations.

K. C. Chambers (IfA), M. E. Huber (IfA),K. W. Smith (QUB),
S. J. Smartt, (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen
(MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare
(QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder
(IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters,
R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB)

We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck
in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553
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  for
more details of filters, photometry, methods etc).

Our reference stack and calibrations provide rapid reliable photometry
with the host removed and we will continue to post updates while it is
visible from Hawaii.  A series of short exposures to avoid sky
saturation in twilight in each of i, z, and y provide average nightly
magnitudes (AB) of 

MJD             i       err 
57983.23	17.24	0.06
57984.24	17.91	0.05
57985.24	18.47	0.08

MJD             z       err 
57983.23	17.26	0.06
57984.24	17.80	0.05
57985.24	18.31	0.06

MJD             y       err 
57983.23	17.38	0.10
57984.24	17.59	0.07
57985.24	18.08	0.07

The decline rate 0.6 mag per day is still consistent with some of the
kilonova models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et
al. 2014). 

The very rapid decline (and weak high energy emission) may explain why
transients of these types have not been recovered and recognised
independently in ground-based wide-field surveys to date, before the
LIGO-Virgo era.

For example at d=100Mpc, this transient would fade from around i=19.2
to 21.7 in four days in i-band (and would be fainter and faster in g,
r and broad composite filters).  Making it difficult to recover and
recognise over multiple nights in "~10^3 deg per night" surveys such
as PTF, Pan-STARRS, La Silla Quest, Skymapper, CRTS.  And well beyond
the wider, shallower, ASASSN and ATLAS sensitivities.

A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration:

We analyzed the Karl G. Jansky VLA observation of the field of the possible optical counterpart 
SSS17a (Coulter et al. LVC GCN  21529
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 ) that started on 2017-Aug-19 22:01:48 UT (Corsi et al. LVC 
GCN 21613
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 ). At a central frequency of ~6 GHz, our preliminary analysis does not show any significant 
emission at the location of the optical candidate (RA= 13:09:48.089, Dec= -23:22:53.35, Coulter et al. 
LVC GCN 21529
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 ) down to a 3-sigma limit of ~22 uJy. We detect the host emission (RA = 13:09:47.704, 
Dec =-23:23:02.45; Alexander et al. LVC GCN 21589
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 ) at a flux level of ~0.3 mJy at 6 GHz.

A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration:

We analyzed a further Karl G. Jansky VLA observation of the field of SSS17a, the possible 
counterpart of G298048 in NGC 4993 identified by Coulter et al. (LVC GCN  21529
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 ). The 
observation started on 2017-Aug-19 22:01:48 UT, ended on 2017-Aug-20 00:01:24 UT, and 
was conducted with the VLA in its C configuration in C-X-Ku-bands. At a central frequency 
of ~9.7 GHz, our preliminary analysis does not show any significant emission at the location 
of the optical candidate SSS17a down to a 3-sigma limit of about 18 uJy. We detect the host 
at a flux level consistent with what measured by Alexander et al. (LVC GCN 21545
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 ). Analysis of 
the data collected in other bands is on-going.

P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.B. Cenko (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), S. Campana (INAF-OAB), E. Troja (NASA/GSFC/UMCP) S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL), D.N. Burrows (PSU), , G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report on behalf of the Swift team:

Swift has continued to monitor the position of the likely EM counterpart to the LVC trigger G298048. We have now collected a total of 19.3 ks at the position of the optical source first reported by Coulter et al. (LVC GCN 21529
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 ).

In the summed data a faint X-ray source is detected at a position of (RA,Dec)=194.45112, -23.3845 degrees which is equivalent to:
RA (J2000.0) = 13h 09m 48.27s
Dec (J2000.0) = -23d 23��� 04.3���

with an uncertainty of 6.4 arcsec (radius, 90% confidence). This source is 11.3 arcsec from the position reported by Coulter et al.

The mean count rate is  6.5 (+2.8,-2.2) e-4 ct/sec which corresponds to a 0.3-10 keV flux of 2.6 (+1.1, -0.9) e-14 erg/cm^2/s. Assuming a distance of 42.5 Mpc (D���Elia et al., LVC Circ. 21592) this corresponds to a luminosity of 5.6 (+2.4, -1.9)e39 erg/s. In the data binned per Swift pointing, the peak detection is at ~twice this level.

At the current time we do not have sufficient statistics to confirm whether the object is variable. We also note that, given the probable radio emission from the host (Alexander, Fong & Berger, LVC Circ. 21548) the host may be a weak AGN, at the current time we cannot rule out the possibility that the X-rays come from the host galaxy rather than the optical afterglow.

Further observations are planned.

M. Shara (AMNH), T. Williams (SAAO), P. Vaisanen (SAAO/SALT), S. Potter
(SAAO), E. Romero Colmenero (SAAO/SALT), S. Crawford (SAAO), D. Buckley
(SAAO), J Cooke (Swinburne), Igor Andreoni (Swinburne), Tyler Pritchard
(Swinburne), Jirong Mao (YNAO)


Spectra of an unresolved source at coordinates RA=197.4504, DEC=-23.3815
near the galaxy NGC 4993, obtained with the Robert Stobie Spectrograph on
the Southern African Large Telescope at UT 17:07:19.703 on 18 August 2017
and at UT 16:58:32.764 on 19 August 2017 during early twilight.   The
spectra extends between 3600-8000 Angstroms with a resolution of ~300.  The
spectra is heavily blended with the host galaxy.  After subtraction of the
host galaxy spectra from the 18 August, the source shows a spectra
increasing in flux from 8000 A to 5000 A, which then decreases in flux
after 4500 A.   The spectra from the 19 August 2017 was taken early
twilight and too noisy to say anything definitive.

B. Gendre (UVI), A. Cucchiara (UVI), D. Morris (UVI), N. Orange
(OrangeWave Innovative Science, LLC), D. Drost (UVI), T. Giblin (USAF
Academy), J. Hakkila (College of Charleston), A. Klotz (IRAP), J. Neff
(NSF), D. Smith (UVI), J. Staff (UVI), P. Thierry (Auragne Observatory),
R. Watlington (UVI), on behalf of the FIGARO collaboration report:

We observed the field of SSS17a (Coulter et al., GCN 21529
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 ; Allam et 
al., GCN 21530
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 ; Yang et al., GCN 21531
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 ), the potential counterpart of 
the LIGO/Virgo event G298048 (GCN 21509
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 ), with the 0.5m Virgin Island 
Robotic Telescope (VIRT) on August the 19th, starting at 23:19 UT. We 
performed a series of exposures in the R and Clear filters, with an 
elevation decreasing from 40 degrees. The weather conditions were good, 
with a mean seeing of 2-3 arcsec.

We detect an excess at the position of the potential counterpart in C 
filter at 23:54 UT. Strong contamination from the nearby galaxy prevents 
a precise brightness estimate without galaxy substraction. Further 
analysis is in progress.

The VIRT is still in its commissioning phase.

This message can be cited.

T.-W. Chen, P. Wiseman, J. Greiner, and P. Schady (all MPE Garching) 
report on behalf of the GROND team:

We observed the field of the transient source SSS17a in NCG 4993 
(RA = 13:09:48.09 DEC = -23:22:53.35, discovered by Coulter et al. 
GCN #21529
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 ), possibly associated with LIGO/Virgo trigger G298048, 
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla 
Observatory (Chile).

Observations started at 23:15 UT on August 19th 2017. They were 
performed at an average seeing of 1.8" and at an average airmass 
of 1.4.

We detected a single point source at the location of the transient, 
although the strong host contribution hinders photometric accuracy.

Based on the first 11.7 min of total exposures in g'r'i'z' and 
13.2 min in JHK, we estimate preliminary magnitudes using aperture
photometry (all in AB system) of

g' = 19.8 +/- 0.2 mag, 
r' = 18.1 +/- 0.1 mag, 
i' = 18.0 +/- 0.1 mag, 
z' = 16.8 +/- 0.1 mag, 
J = 16.4 +/- 0.2 mag, 
H = 16.6 +/- 0.2 mag, and 
K = 16.6 +/- 0.2 mag.

We confirm that the transient significantly declines in optical 
brightness (Yoshida et al. GCN #21586
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 , Chambers et al. GCN #21590
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 ,
Tominaga et al. GCN #21595
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 , Melandri et al. GCN #21596
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 , Im et al. 
GCN #21597
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 , Valenti et al. GCN #21606
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 ), but the transient keeps 
flat in z'JHK-band brightness for 1 day compared to our previous 
report (Wiseman et al. GCN #21584
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 ).

Given magnitudes are calibrated against Pan-STARRS1 field stars 
as well as 2MASS field stars and are not corrected for the expected 
Galactic foreground extinction corresponding to a reddening of 
E_(B-V)= 0.1 mag in the direction of the candidate (Schlafly & 
Finkbeiner 2011).

We acknowledge the excellent help in obtaining these data from 
Angela Hempel on La Silla.

Stefano Valenti (UC Davis), Sheng Yang (INAF-OAPd, UC Davis), David Sand 
(UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), 
Dan Reichart, Josh Haislip, Vladimir Kouprianov (UNC) report on behalf 
of the Gravitational Wave Follow-Up by DLT40.

We continued to monitor DLT17ck/SSS17a (GCN 21529
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 ;GCN21530; GCN21531
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 ), 
the electromagnetic counterpart candidate of the LIGO/Virgo GW G298048 
(GCN21509
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 ).
Following the optical observations reported for DLT17ck/SSS17a 
(GCN21579
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 ; GCN21531
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 ; GCN21567
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 ; GCN21541
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 ; GCN21590
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 ; GCN21553
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 ; GCN21560
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 ; 
GCN21584
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 ; GCN21580
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 ; GCN21583
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 ; GCN21590
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 ; GCN21595
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 ; GCN21597
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 ), here we 
report that DLT17ck/SSS17a is continuing fading.
Using data from the PROMPT 5 0.41m telescope located at CTIO, DLT40 
observation began at 2017 August 19.99 UT and shows the source at 
magnitude r = 18.96 �� 0.10 mag. We also observed DLT17ck in i and z, for 
which analysis is under way.

K. De (Caltech), M. M. Kasliwal (Caltech), V. Bhalerao (IIT-B), P. Chandra
(NCRA), A. Corsi (TTU)

report on behalf of the GROWTH (Global Relay of Observatories Watching
Transients Happen) collaboration

We observed SSS17a (GCN 21529
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 ) with the Giant Meterwave Radio Telescope in
India at 610 MHz on UT 2017-08-18 11:00. We do not detect any emission at
this location. Multi-band multi-epoch follow-up is underway. We thank the
GMRT staff for rapidly scheduling these observations. The GMRT is run by
the National Centre for Radio Astrophysics of the Tata Institute of
Fundamental Research.

D. Rabinowitz and C. Baltay (Yale) report:

The La Silla - QUEST supernova survey (conducted with the 160-Megapixel
QUEST camera on the ESO 1.0m Schmidt at La Silla, Chile from 2010 to 2016)
covered the location of SSS17a (Coulter et al. LVC GCN 21529
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 ) with 345
exposures to depth ~R=19 in the years 2013 to 2016 (~100 exposures per
year). Visual inspection of these images at the location of SSS17a shows
no point source to limit ~R=18.

[GCN OPS NOTE(18aug17):  Per submitter's and author's request, the submitter
was changed from Singer to Rabinowitz to work around a momentary problem.]

A. Grado (INAF-OAC), E. Cappellaro (INAF-OAPD), G. Greco (Urbino
University/INFN Firenze), M. Branchesi (GSSI), S. Covino
(INAF-OAB), P. D'Avanzo (INAF-OAB), F. Getman (INAF-OAC), A. Melandri
(INAF-OAB), L. Amati
(INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S.
Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC),  S. Campana (INAF-OAB), V.
D'Elia (INAF-ASDC), D. Fugazza, L. Limatola (INAF-OAC), M. Lisi (INAF-OAR),
L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa),
S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P.
Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G.
Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S.
Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave
Inaf TeAm report:


Observations of 9 square degrees of the skymap of the Advanced LIGO and
Virgo trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) were performed with the
VLT
Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal equipped
with OMEGACAM (FOV=1 square degree). The observation of the 3 x 3 square
degrees region
is centered on the following  coordinates:

RA, Dec (ICRSd):

194.30420 -17.85690

The VST pointings was generated using the GWsky script (
https://github.com/ggreco77/GWsky). Starting from the high probability
region of the skymap, the sequence was defined to maximize the contained
localization probability.
The images were taken in the r_SDSS filter with an exposure of 80s (split
in two dithered exposures of 40 s each). The observations started at
2017-08-17T 23:44:50.964 UTC and finished at 2017-08-18T 00:08:46.388.
Automatic data reduction with the VSTTube pipeline (Grado et al. 2012
Mem.SAIt 19, 362 ) was completed. The image analysis is ongoing.

M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim, C.-W. Lee (KASI) on
behalf of the KU collaboration



We continued to observe the optical counterpart candidate of LIGO/Virgo
G298048 (LVC GCNs 210505
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 , 21509
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 , 21513
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 ), SSS17a (Coutler et al. LVC GCN
21529
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 ), using the KMTNet 1.5m telescopes and other small telescopes. KMTNet
is an observing system made of three 1.5m telescopes at the Siding Spring
Observatory (SSO), the South African Astronomical Observatory (SAAO), and
the Cerro-Tololo Inter-American Observatory (CTIO). BVRI images were taken
at each KMTNet site in 2017-08-18 and 08-19 UT.

Preliminary magnitudes in R-band shows continued dimming of SSS17a (e.g.,
Im et al. LVC GCN 21566
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 ), and more interestingly, SSR17a seems to be fading
faster in the last epoch data taken at SSO (see also Melandri et al. LVC
GCN 21596
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 ).

UT R (mag) Site

2017-08-18.71 17.4 +- 0.1 SAAO

2017-08-18.98 17.7 +- 0.1 CTIO

2017-08-19.35 18.4 +- 0.2 SSO

The observation using small telescopes at SSO was carried out too (see Im
et al. LVC GCN 21563
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 ), and the images taken with these telescopes also
suggest faster dimming. The observations using the KMTNet telescopes and
the small telescopes are ongoing.

A. Melandri, P. D'Avanzo, S. Campana, S. Covino (INAF-OAB), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report:


We continued the optical/NIR follow-up monitoring of the LIGO/Virgo GW trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile) by performing targeted observations of catalogued galaxies in the LVC skymap. The observations were carried out from 23:31 UT on 2017 Aug 18 to 01:18 UT on on 2017 Aug 19, simultaneously in the g, r, i, z, J, H and K bands.

We clearly detect in all bands the optical source reported by Coulter et al. (LVC GCN 21529
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 , 21567
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 ), Allam et al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 , 21579
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 ), Melandri et al. (LVC GCN 21532
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 ), Arcavi et al. (LVC GCN 21538
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 , 21581
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 ), Nicholl et al. (LVC GCN 21541
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 , 21580
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 ), Tanvir & Levan (LVC GCN 21544
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 ), Evans et al. (LVC GCN 21550
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 ), Simon et al.(LVC GCN 21551
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 ), Singer et al. (LVC GCN 21552
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 ), Chambers et al. (LVC GCN 21553
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 , 21590
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 ), wolf et al. (LVC GCN 21560
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 ), Yoshida et al. (LVC GCN 21561
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 , 21586
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 ), Kilpatrick et al. (LVC GCN 21583
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 ) and Wieseman et al. (LVC GCN 21584
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 ).

With respect to our previous epoch (Melandri et al. LVC GCN 21532
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 ), preliminary analysis shows that the source is significantly fainter in the g-band and displays no variation in the r-band. Analysis and calibration is ongoing and further observations are planned.

Tominaga, N. (Konan Univ.), Yoshida, M., Tanaka, M., Terai, T., Nakata, F.,
Furusawa, H., Koshida, S. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima Univ.),
Motohara, K., Ohsawa, R., Morokuma, T., Yasuda, N. (Univ. of Tokyo),
Kawai, N. (Tokyo Tech), and Asakura, Y. (Nagoya Univ.) on behalf of the
J-GEM collaboration

We performed z-band imaging observations for the gravitational wave event
G298048 (GCN 21505
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 ; 21509; 21513) with Hyper Suprime-Cam attached to the
Subaru telescope on August 19 2017 UT (Yoshida et al. GCN 21586
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 ).

We made photometric calibration with Pan-STARRS1 catalog (Chambers et al.
2016) using HSC pipeline (Bosch et al. 2017) and obtained psf magnitude
of SSS17a (Coulter et al. 2017; GCN 21529
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 ) as

        z = 17.8 (AB) (2017-08-19 05:26--05:52UT),

which is 0.5 mag fainter than the psf magnitude obtained with Subaru/HSC 
on August 18 UT (Yoshida et al. GCN 21561
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 ). The fading nature of SSS17a 
in the z-band is consistent with the reports in Nicholl et al. (GCN 21580
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 ) 
and Chambers et al. (GCN 21590
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 ).

K. Wiersema (University of Leicester), S. Covino (INAF-OAB),  A. Melandri 
(INAF-OAB) and  E. Palazzi (INAF-IAFS Bo) report on behalf of a large 
collaboration:

We obtained optical linear polarimetry measurements of object SSS17a
(Coulter et al., GCN 21529
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 ; Allam et al., GCN 21530
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 ; Yang et al., GCN 21531
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 ,
Melandri et al., GCN 21532
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 ) possibly associated with the LIGO/Virgo event
G298048 (GCN 21509
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 ). We used the ESO Very Large Telescope UT1 (Antu)
equipped with the FORS2 instrument.  Observations started on 23:09 UT
on 18 August 2017, i.e. during twilight, and continued until the
source reached airmass 2.

FORS2 uses a Wollaston element and a rotating halfwave plate to perform
imaging polarimetry; additionally we used the FORS2 R_special filter (similar
to R) . We obtained a large series of imaging polarimetry datasets, each
consisting of 4 angles of the wave plate, using exposure times of 60 seconds
for each exposure; the transient is bright in our data.
In a preliminary analysis of a subset of our data, we find no evidence of optical
linear polarisation, with a preliminary upper limit on the linear polarisation of
P_linear < 1%. We expect this value to change somewhat through a more thorough
 analysis in the future, e.g. using more accurate models to correct for the
host galaxy emission and rapidly varying twilight contribution.

Our polarisation limit is a first for a kilonova candidate, and indicates a relatively
smooth emission region, with no evidence of significant asymmetry at the time
of observations. Similarly, this limit may indicate that there is no large contribution
of non-thermal emission in the observed wavelength at the time of observations.

We acknowledge excellent support from the ESO staff, J. M. Corral-Santana and
S. Brilliant, and in particular the visiting observer, M. Lendl,  who so kindly gave
up some of their observing time.

E. Pian (INAF-IASF Bo), V. D'Elia (INAF-ASDC),  S. Piranomonte (INAF-OAR), M.  Branchesi (GSSI), S. Campana (INAF-OAB), E. Cappellaro (INAF-OAPD), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Grado (INAF-OAC), G. Greco (Urbino University/INFN Firenze), A. Melandri (INAF-OAB), E. Palazzi (INAF-IASF Bo), G.  Stratta (Urbino University/INFN Firenze), L . Tomasella (INAF-OAPD), L.  Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S.  Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), D. Fugazza, F. Getman (INAF-OAC), L.  Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), L.  Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G.  Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), S. Yang (INAF-OAPD), L. Sbordone (ESO) and  E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm and the team of the ESO VLT program 099.D-0382(A) report:

We observed object SSS17a (Coulter et al., GCN 21529
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 ; Allam et al., GCN 21530
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 ; Yang et al., GCN 21531
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 , Melandri et al., GCN 21532
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 ) possibly associated with the LIGO/Virgo event G298048 (GCN 21509
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 ), with the ESO Very Large Telescope UT 2 (Kueyen) equipped with the X-shooter spectrograph, covering the wavelength range 3000-25000 AA. Observations started at 23:16 UT on 2017-08-18, during the twilight, roughly 1.5 days after the burst and consisted of 4 exposures of 600 s each.

The transient is bright, well detected in the acquisition image, and clearly visible in all the spectral range. After a preliminary reduction the continuum appears to be similar to that predicted by kilonova models (Tanaka & Hotokezaka 2013, ApJ, 775, 113; Kasen et al. 2015, MNRAS, 450, 1777, Rosswog et al. 2016, arxiv1611.09822). We do not detect any obvious emission lines throughout the spectrum.

Further X-shooter observations are planned.

We acknowledge excellent support from the ESO observing staff in Paranal, in particular N. Jimenez and S. Brillant.

[GCN OPS NOTE(20aug17): Per author's request, (a) the 1st & 2nd authors exchanged order, (b) a couple other changes in the rest of the author list, and (c) LS was removed the 4th paragraph.]
[GCN OPS NOTE(21aug17): Per author's request (D'Elia), G. Greco was added to the author list.]
[GCN OPS NOTE(16sep17): Per author's request (Pian), (a) the phrase "and tentative redshift of SSS17a" was removed from the Subject-line, and (b) the last 4 sentences in the second paragraph were removed.]

D. Malesani (DARK/NBI), E. Pian (INAF-IASF Bo), J. Hjorth (DARK/NBI), D. 
J. Watson (DARK/NBI), L. Amati (INAF-IASF Bo), L. A. Antonelli, 
(INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. 
Botticella (INAF-OAC), M. Branchesi (GSSI), S. Campana (INAF-OAB), E. 
Cappellaro (INAF-OAPD), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), V. 
D'Elia (INAF-ASDC), D. Fugazza (INAF-OAB), F. Getman (INAF-OAC), A. 
Grado (INAF-OAC), G. Greco (Urbino University/INFN Firenze), L. Limatola 
(INAF-OAC), M. Lisi (INAF-OAR), A. Melandri (INAF-OAB), L. Nicastro 
(INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), S. Piranomonte (INAF-OAR), L. 
Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. 
Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. 
Testa (INAF-OAR), L. Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. 
Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report:


We observed object SSS17a (Coulter et al., GCN 21529
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 ; Allam et al., GCN 
21530
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 ; Yang et al., GCN 21531
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 ) possibly associated with the LIGO/Virgo 
event G298048 (GCN 21509
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 ), using the Nordic Optical Telescope located in 
La Palma (Canary Islands, Spain).

Observations were carried out around Aug 18.85 UT (1.32 days after the 
GW event), and consisted of 9 min exposure in each of the J and K 
filters. Conditions were difficult due to the large airmass (4.0 to 5.5) 
and the still bright twilight sky, which led to an unusually elongated 
PSF due to imperfect focusing.

SSS17a is well visible in the J image and faintly detected in K. Based 
on the 2MASS catalog, we provide preliminary magnitudes J = 16.23 +- 
0.11 and K = 15.88 +- 0.25 (both Vega). We note that an extra error may 
arise from the non-circular PSF and the uneven background around the 
nearby NGC 4993.

Our fluxes are earlier and fainter than the GROND measurements (Wiseman 
et al., GCN 21584
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 ), confirming the brightening of SSS17a at NIR 
wavelengths and the overall cooling trend noted by several authors 
(e.g., Cenko et al., GCN 21572
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 ; Lyman et al., GCN 21582
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 ; Wiseman et al., 
GCN 21584
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 ).

We acknowledge excellent support of the NOT visiting observer, Auni 
Somero, in carrying out this difficult observation.

K. C. Chambers (IfA), S. J. Smartt, (QUB), M. E. Huber (IfA),
K. W. Smith (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen
(MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare
(QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder
(IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters,
R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB)

We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck
in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553
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  for
more details of filters, photometry, methods etc).

Our reference stack and calibrations provide rapid reliable photometry
with the host removed and we will continue to post updates while it is
visible from Hawaii.  A series of short exposures to avoid sky
saturation in twilight in each of i, z, and y provide average nightly
magnitudes (AB) of 

MJD             i       err 
57983.23	17.24	0.06
57984.24	17.91	0.05

MJD             z       err 
57983.23	17.26	0.06
57984.24	17.80	0.05

MJD             y       err 
57983.23	17.38	0.10
57984.24	17.59	0.07

This confirms the fading seen in the DECam images (Nicholl et
al. GCN 21580
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 ), and is consistent with the other reports of fading (e.g. Yoshida et al. GCN
21586
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 , Yang et al. 21579,  Arcavi et al. 21581).

The fading in i-band and bluer bands is clearly more pronounced than
in y-band and distinct from the rising NIR (Wiseman et al GCN 21584
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 ). 

This rate of fading is quantitatively similar to that of the kilonova
or merging NS models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et
al. 2014). And is uncommon for the populations of known nearby
transients.

K.D. Alexander (Harvard), W. Fong (Northwestern), and E. Berger (Harvard)
report on behalf of a larger collaboration:

We analyzed observations taken with the Very Large Array beginning on 2017
Aug 18 at 22:04:57 UT (1.39 d after the Fermi trigger time; Blackburn et
al., LVC GCN 21506
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 ). In two hours of observations at a mean frequency of
10.0 GHz, we detect the source reported in our previous VLA observations
(Alexander et al., LVC GCN 21545
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 ; 21548) and in ATCA observations
(Bannister et al., LVC GCN 21559
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 ) at a similar flux level. We measure an
improved position of:

RA = 13:09:47.704

Dec =-23:23:02.45

with an uncertainty of 0.1��� in each coordinate. We note that the beam size
in our images is 3.1��� by 1.4���, significantly smaller than our previous VLA
observations. The lack of variability over a 19.9 hr period along with full
spatial coincidence with NGC 4993 indicates that this radio emission is
originating from the host galaxy.

We further note that there is no detected emission at the position of the
optical transient (Coulter et al., LVC GCN 21529
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 ) down to a 3-sigma limit
of 17 microJy.

A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni (Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav), D. Dobie (University of Sydney), D. Kaplan (UWM) C. Lynch (University of Sydney), T. Murphy (University of Sydney), on behalf of a joint effort between OzGrav and the VAST collaboration.



We are observing the optical transient SSS17a (Coulter et al. - GCN 21529
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 , Allam et al. - GCN 21530
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 , Yang et al.- GCN 21531
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 , Melandri et al. - GCN 21532
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 ) and its host galaxy NGC 4993 with the Very Long Baseline Array.

 
We are observing at a central frequency of 8.7 GHz with a bandwidth of 256 MHz.

The first observation took place from 2017-08-17 19:58UT to 2017-08-18 01:34UT.  

Analysis of the data will take place after correlation, in 7-10 days.  

Two subsequent epochs are planned in the coming three days.

We thank the Long Baseline Observatory staff for facilitating these observations.

V.M.Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, 
D.Kuvshinov, P.Balanutsa,  O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov
Lomonosov Moscow State University, Sternberg Astronomical Institute

D.Buckley, S.Potter, M.Kotze,
South African Astronomical Observatory

R.Podesta, C.Lopez, F.Podesta
Observatorio Astronomico Felix Aguilar (OAFA) , National University of San
Juan, Argentina

H.Levato, C.Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina

N.M. Budnev, O. Gress, K. Ivanov, S.Yazev
Irkutsk State University

V.Yurkov, Yu.Sergienko, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu
The Instituto de Astrofisica de Canarias

A. Tlatov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

As we reported in LVC GCN 21546
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  MASTER-OAFA have imaged the BAYESTAR 
localization map of LIGO/Virgo G298048 (GCN 21513
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 ).

MASTER-SAAO  have new images of  NGC 4993 galaxy starting 2017-08-18 17:06:55 
UT in B, R and unfiletred with magnitude limit 19.8 (Lipunov et al., LVC 
GCN 21570
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 ). We see
object in B, R and unfiltered images detected by Coulter et al. (LVC GCN 
21529
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 ), Allam et  al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 ), 
Melandri et al.  (LVC GCN 21532
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 ), Lipunov et al., (LVC GCN 21546
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 ).

B = 18.5 +- 0.2
R = 17.5 +- 0.2
W = 18.0 +- 0.2

The unfiltered magnitude not changed with respect to first observations 
(Lipunov et al., LVC GCN 21546
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 )

This message can be citted.

Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Tajitsu, A.,
Fujiyoshi, T. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima U.),
Tominaga, N. (Konan U.), Motohara, K., Ohsawa, R., Morokuma, T.
(Univ. of Tokyo), Kawai, N. (Tokyo Tech.), and Asakura, Y. (Nagoya
Univ.) on behalf of the J-GEM collaboration

We performed follow-up observations for the gravitational wave
event G298048 with Hyper Suprime-Cam attached to the Subaru
telescope from 5:20 to 6:00 on August 19 2017 UT. We surveyed the
same sky area as our previous observation (GCN 21549
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 ) with HSC-z
band filter. SSS17a, which is the most promising candidate of the
optical counterpart of G298048 (GCN 21529
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 ), was still bright. The
rough estimation of the z-band magnitude of the object was ~17.7
(AB). Further analysis is ongoing.

The sky fields observed by this survey are listed below:

ID Time��������������� RA��������� DEC��������� Exp� Filter
-----------------------------------------------------------
28 2017-08-19T05:21:42 13h10m14.4s -23d19m20.0s� 2.0s HSC-z
04 2017-08-19T05:22:21 13h07m25.6s -26d36m51.9s 10.0s HSC-z
05 2017-08-19T05:23:02 13h10m14.3s -27d17m02.1s 10.0s HSC-z
06 2017-08-19T05:23:46 13h13m03.0s -27d57m27.1s 10.0s HSC-z
07 2017-08-19T05:24:28 13h15m51.8s -28d38m07.2s 10.0s HSC-z
08 2017-08-19T05:25:11 13h18m40.5s -29d19m03.0s 10.0s HSC-z
09 2017-08-19T05:25:57 13h21m29.2s -30d00m15.5s 10.0s HSC-z
28 2017-08-19T05:26:44 13h10m14.4s -23d19m20.0s 30.0s HSC-z
10 2017-08-19T05:27:44 13h04m36.9s -24d37m43.0s 30.0s HSC-z
11 2017-08-19T05:28:45 13h07m25.6s -25d17m13.0s 30.0s HSC-z
12 2017-08-19T05:29:47 13h10m14.4s -25d56m55.7s 30.0s HSC-z
13 2017-08-19T05:30:48 13h13m03.1s -26d36m52.0s 30.0s HSC-z
28 2017-08-19T05:31:49 13h10m14.4s -23d19m20.0s 30.0s HSC-z
14 2017-08-19T05:32:51 13h01m48.2s -22d40m26.0s 30.0s HSC-z
15 2017-08-19T05:33:54 13h15m51.8s -27d17m02.0s 30.0s HSC-z
16 2017-08-19T05:34:55 13h18m40.5s -27d57m27.0s 30.0s HSC-z
17 2017-08-19T05:35:59 13h04m36.9s -23d19m20.1s 30.0s HSC-z
18 2017-08-19T05:37:00 13h07m25.7s -23d58m25.6s 30.0s HSC-z
19 2017-08-19T05:38:02 12h58m59.5s -20d44m48.0s 30.0s HSC-z
20 2017-08-19T05:39:03 13h10m14.4s -24d37m43.1s 30.0s HSC-z
22 2017-08-19T05:40:05 13h13m03.1s -25d17m12.9s 30.0s HSC-z
23 2017-08-19T05:41:06 13h15m51.9s -25d56m55.6s 30.0s HSC-z
24 2017-08-19T05:42:15 12h56m10.8s -18d50m37.3s 30.0s HSC-z
25 2017-08-19T05:43:15 13h04m37.0s -22d01m43.1s 30.0s HSC-z
26 2017-08-19T05:44:15 13h07m25.7s -22d40m26.2s 30.0s HSC-z
29 2017-08-19T05:45:16 13h01m48.3s -20d06m35.2s 30.0s HSC-z
28 2017-08-19T05:46:17 13h10m14.4s -23d19m20.1s 30.0s HSC-z
28 2017-08-19T05:47:17 13h10m14.4s -23d19m20.1s 120.0s HSC-z
28 2017-08-19T05:49:48 13h10m14.4s -23d19m20.0s 120.0s HSC-z
28 2017-08-19T05:52:20 13h10m17.5s -23d18m06.5s 60.0s HSC-z
-----------------------------------------------------------

M. Nicholl (Harvard), C. Briceno (CTIO), P. Cowperthwaite (Harvard), 
E. Berger (Harvard), J. Elias (NOAO), S. Heathcote (CTIO),
J. Annis (Fermilab), D. Tucker (Fermilab), M. Soares-Santos (Brandeis),
R. Kessler (U Chicago), M Sako (U Penn)

We report optical spectroscopy of SSS17a, the counterpart to G298048, using 
the Goodman Spectrograph on the 4m SOAR telescope on 2017-08-18 starting 
at UT 23:23:38. This is ~1.5 days after the LIGO and Fermi signals. 

Previous spectra were obtained by Drout et al (GCN 21547
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 ) and more recently
Lyman et al (GCN 21582
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 ). We confirm some of the results of Lyman et al: a peak 
between 5000-6000 Angs, rapid fall-off in the blue, and no match to known 
supernova types. The colour temperature is best matched by a blackbody with 
T~5000K, after dereddening by a Milky Way E(B-V)=0.1053. The UV flux appears
suppressed relative to a simple blackbody.

This shows significant cooling compared to T~8000K one day previous, as
reported by Malesani et al (GCN 21577
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 ) and Cowperthwaite et al (GCN 21578
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 ).
The blackbody radius (~8e14 cm) indicates an average velocity ~0.1c, suggesting
the expansion has now slowed compared to those earlier estimates (0.2-0.3c).

We note the possibility of weak, broad bumps at ~5000 and ~6000 Ang in our
quick extractions.


=======================
Matt Nicholl
Postdoctoral Research Fellow
Harvard-Smithsonian Center
for Astrophysics
mattnicholl.net
=======================

P. Wiseman, T.-W. Chen, J. Greiner, and P. Schady (all MPE Garching)
report on behalf of the GROND team:

We observed the field of the of the transient source SSS17a in NCG 4993 
(RA =
13:09:48.09 DEC = -23:22:53.35, Coulter et al. GCN #21529
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 , Allam et al. 
GCN
#21530
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 , Yang et al. GCN #21531
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 , Melandri et al. GCN #21532
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 ), possibly 
associated
with LIGO/Virgo trigger G298048, simultaneously in g'r'i'z'JHK with 
GROND (Greiner
et al. 2008,PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La 
Silla
Observatory(Chile).

Observations started at 23:15 UT on August 18th 2017. They were 
performed at an
average seeing of 1.8" and at an average airmass of 1.4.

We clearly detect a single point source at the location of the 
transient, although
  the strong host contribution hinders photometric accuracy.

Based on the first 13.8 min of total exposures in g'r'i'z' and 12.4 min 
in JHK, we
estimate preliminary magnitudes (all in AB system) of

g' = 17.9 +/- 0.1 mag,
r' = 17.2 +/- 0.1 mag,
i' = 17.2 +/- 0.1 mag,
z' = 16.8 +/- 0.1 mag,
J = 16.6 +/- 0.2 mag,
H = 16.9 +/- 0.2 mag, and
K = 16.8 +/- 0.2 mag.

There appears to be little change in the optical brightness of the 
source: we
compare our magnitudes to the  g = 17.76 mag and r = 17.20 mag from 14 
hours
previous,reported by SkyMapper (Wolf et al. GCN #21560
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 ); and to the i,z 
= 17.25
mag of Pan-STARRS (Chambers et al. GCN #21553
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 ) and z = 17.3 from HSC-z 
(Yoshida
et al. GCN #21561
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 ) from 19 hours previous.

On the other hand, the object has brightened significantly in the NIR 
over the
last 24 hours. We compare the J band to the value of 17.5 mag (AB) from
VISTA/VIRCAM reported by Tanvir et al. (GCN #21544
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 ), while the K band 
(now 14.9
in Vega) is much brighter than the 16.9 mag (Vega) reported by Singer 
et al.
(GCN #21552
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 ).

Given magnitudes are calibrated against Pan-STARRS zeropoints/2MASS 
field stars
and are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)= 0.1 mag in the direction of 
the
candidate (Schlafly & Finkbeiner 2011).

After the Milky Way extinction correction, we fitted our colour SED 
assuming a
black body (no K-correction applied), which indicates a temperature of 
5333 +/-
243 K.

C. D. Kilpatrick, D. A. Coulter, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, A. L. Piro (Carnegie), A. Rest (STScI)

report on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration:

We obtained imaging in B, V, and i bands of SSS17a (Coulter et al., LVC GCN 21529
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 ) on 2017 Aug 19 UT with the 1-m Swope telescope at Las Campanas Observatory.  We calibrated these data using approximately 90 B, V, and i' APASS standards in the same field as SSS17a and report the following preliminary photometry:

B = 18.8 mag +/- 0.1 mag
V = 18.1 mag +/- 0.1 mag
i = 17.4 mag +/- 0.1 mag

Additional photometry is being obtained and analyzed.

J. Lyman (Univ. of Warwick), D. Homan (Univ. of Edinburgh), K. Maguire
(QUB), M. T. Botticella (INAF-Capodimonte), M. Fraser (UCD), C.
Inserra (Southampton), E. Kankare (QUB), S. J. Smartt (QUB), K. W.
Smith (QUB), M. Sullivan (Southampton), S. Valenti (UC Davis), O.
Yaron (Weizmann), I. Manulis (Weizmann), D. Young (QUB), T.-W. Chen
(MPE), S. Campana (INAF-Brera), S. Benetti, L. Tomasella
(INAF-Padova), G. Leloudas (DARK, Copenhagen), Z. Cano (IAA, Granada).

Under the extended Public extened ESO Spectroscopic Survey for
Transient Objects (ePESSTO; see Smartt et al. 2015, A&A, 579, 40
http://www.pessto.org), we report spectra of the optical/NIR candiate
counterpart of the gravitational wave source G298048 in NGC4993.

This object was discovered by Coulter et al. (GCN 21529
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 , named SSS17a)
and further detected by Allam et al. (GCN 21530
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 ), Yang et al. (GCN
21531
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 ), Melandri et al. (GCN 21532
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 ), Nicholl et al. (GCN21541
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 ), Tanvir
& Levan (GCN21544
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 ), Chambers et al. (GCN 21553
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 ), Yoshida et al. (GCN
21549
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 ).

The observations were performed on the ESO New Technology Telescope at
La Silla with the EFOSC2 instrument in spectroscopic mode starting
from 2018-08-18 at 23:20 UT, using the Gr11 and Gr16 which provide
coverage 3345-9995 at a resolution between 260-396 (v = 1150 - 756
km/s) for a 1.5" slit, which was used in roughly 1.5-2.0" seeing. 

Quick look reductions (not including fringe and flat correction)
indicate the spectrum is highly unusual for a nearby transient. 

We have dereddening the spectrum with A_v = 0.34, for Milky 
Way correction. 

The continuum is featureless, similar to the report of the first
Magellan spectrum in Drout et al. (GCN 21547
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 ). But it peaks at 5500
and falls off rapidly in the blue. This is consistent with the Swift
colours reported and the fading U-band and UV flux. The red part
(beyond 5000Angs) can be fit with a black-body temperature of around
6000K or a power law.  But neither are consistent with the turn over
in the blue.  There are no strong features in the blue that indicate
line absorption or could be identified with known transitions.  There
are no Balmer lines, no Ca II H&K, or Si II absorption seen in
supernova-like transients. 

We can certainly conclude this is not a young supernova of any type in
this host, nor is it consistent with being a background supernova of 
any standard type. The UV dimming and maintaining of the red and NIR
flux appears broadly consistent with many flavours of kilonova models. 

Further observations with ePESSTO will continue over the next 4
nights, combining EFOSC2 and SOFI observations. During the 5 years of
PESSTO spectroscopic surveys, this transient stands out as exceptional
in its colours, evolution and spectra (supporting the ideas in Foley
GCN 21557
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 ).

I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las
Cumbres Obs), D. Poznanski, M. Zalzman (TAU), L.P. Singer (NASA/GSFC), S.
Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley), W.
Fong (Northwestern) and D. Maoz (TAU) report the sudden fading of SSS17a /
DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC
GCN 21529
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 ) and others.

In the course of Las Cumbres Observatory LIGO followup we have now
accumulated four epochs of the possible counterpart SSS17a / DLT17ck in the
last 24 hours from our telescopes in the Cerro Tololo Inter-American
Observatory (Chile), the Siding Spring Observatory (Australia) and the
South African Astronomical Observatory (South Africa).

Using aperture photometry in the wide w-band (=g+r+i), we see the transient
first brighten by 0.12 magnitudes (as reported in Arcavi et al. LVC GCN
21565
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 ) and then fade by ~0.2 magnitudes:

Time (UT)         Site          Relative w-band Magnitude
2017-08-18 00:15  Chile         0
2017-08-18 09:10  Australia     -0.12 +- 0.02
2017-08-18 17:35  South Africa  +0.19 +- 0.04
2017-08-18 23:13  Chile         +0.22 +- 0.13

Further observations (including other bands) and analysis are ongoing.

M. Nicholl (Harvard), P. S. Cowperthwaite (Harvard), E. Berger (Harvard),
P. K. G. Williams (Harvard), S. Allam (Fermilab), J. Annis (Fermilab), J.
Garcia Bellido (IFT CSIC/UAM), D. J. Brout (UPenn), D. Brown (Syracuse), R.
E. Butler (Fermilab), H.-Y. Chen (Harvard), R. Chornock (Ohio University),
E. Cook (TAMU), , H. T. Diehl (Fermilab),
A. Drlica-Wagner (Fermilab), Z. Doctor (U. Chicago), M. R. Drout
(Carnegie), B. Farr (U Chicago), R. J. Foley (UCSC), W. Fong
(Northwestern), D. Fox (Penn State), J. Frieman (Fermilab/UChicago), M.S.S.
Gill (Stanford), R. Gruendl (NCSA), K. Herner (Fermilab), D. Holz (UChicago),
R. Kessler (UChicago), H. Lin (Fermilab), J. Marriner (Fermilab), R.
Margutti (Northwestern), J. Marshall (TAMU), E. Neilsen (Fermilab), F.
Paz-Chincon (NCSA), A. Rest (STScI), M. Sako (UPenn), D. Scolnic (KICP), N.
Smith (Arizona), M. Soares-Santos (BrandeisU), D. Tucker (Fermilab), V. A.
Villar (Harvard), A. Walker (NOAO), B. Yanny (Fermilab), P. Lopes (UFRJ),
F. Durret (IAP), A. Louren��o (UFRJ)

On behalf of the DESGW+community team:

We report further i- and z-band photometry from DECam imaging of
the possible optical counterpart to G298048 first identified in Coulter et
al. (LVC GCN 21529
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 ), and further reported on by Allam et al. (LVC GCN
21530
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 ), Valenti et al. (LVC GCN 21531
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 ), Melandri et al. (LVC GCN 21532
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 ) and
Arcavi et al. (GCN 21538
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 ). Observations were obtained on 2017-08-19 at
23:23 UTC.

We find preliminary PSF magnitudes of

i = 17.8 +/- 0.1 mag
z = 17.6 +/- 0.1. mag

In images obtained the previous night (2017-08-18 at 00:04 UT), we measured
i ~ z ~ 17.5 mag (Nicholl et al., LVC GCN 21541
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 ). This indicates a fading
of
~0.3 mag in i-band over the course of 1 day. This value is consistent with
that
expected for an afterglow or rapidly-evolving kilonova.

These magnitudes are determined from differential PSF photometry of DECam
images relative to Pan-STARRs 3pi catalogs.

Further analysis is ongoing.

Sheng Yang (INAF-OAPd, UC Davis), Stefano Valenti(UC Davis), David Sand (UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), Dan Reichart, Josh Haislip (UNC) report on behalf of the Gravitational Wave Follow-Up by DLT40.

We report the second epoch for DLT17ck/SSS17a, the possible counterpart of G298048 in NGC 4993 detected by Coulter et al. (LVC GCN  21529
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 ), Allam et  al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 ), Melandri et al. (LVC GCN 21532
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 ), Arcavi et al. (LVC GCN 21538
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 ), Lipunov et al., (LVC GCN 21546
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 ). Using data from the PROMPT 5 0.41m telescope located at CTIO, DLT40 observation began at 2017 August 18.99 UT and shows the source at magnitude R = 18.00 +/- 0.06 mag. Compared with our discovery detections, R~17.3 mag in Yang et al. (LVC GCN 21531
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 ), the source is declining. We also report last our non-detection at 2017 July 27.99 UT, during the monitoring of NGC4993 with the DLT40 search. The magnitude limit is up to 19.1 mag (open filter scaled to r band).

P.S. Cowperthwaite (Harvard), M. Nicholl (Harvard), E. Berger (Harvard)

We construct a preliminary UV/Optical/NIR SED for the potential optical
counterpart SSS17a first reported by Coulter et al. (GCN 21529
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 ). These data
are compiled from the photometry reported in circulars submitted during the
first night of follow-up. We correct these data for extinction due to
reddening along the line of sight to the host galaxy NGC 4993.

We perform a preliminary fit with a blackbody function to this SED finding
an effective temperature of T = 8000 K and an effective radius of R = 6e14
cm.

We test the sensitivity of our fit to the UV flux, refitting with the
Swift/UVOT data excluded. We find T = 10,200 K and R ~ 4e14 cm.

In both cases, the large expansion radius and short time since explosion (t
~ 1 day) suggest an expansion velocity of >0.2c. This is too fast to be
explained by supernova ejecta, but is consistent with the expansion
velocities expected for relativistic BNS/NS-BH merger ejecta.

These values, and the inferred relativistic expansion, are consistent with
the results of Malesani et al. (GCN 21577
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 ).

Daniele Malesani, Darach Watson, and Jens Hjorth (all DARK/NBI), report:

Analysis of the optical and near-infrared data reported through the GCNs 
allows to build the spectral energy distribution of the candidate 
optical counterpart (Coulter et al., GCN 21529
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 ; Allam et al., GCN 21530
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 ; 
Yang et al., GCN 21531
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 ) of the LIGO/Virgo event G298048 (GCN 21509
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 ). A 
standard Galactic extinction curve with A_V = 0.34 has been adopted but 
no rest-frame extinction has been included.

We caution that the available data are based on a preliminary analysis 
and are not always strictly simultaneous, though the reported 
variability (at least in the optical) is modest (Arcavi et al., GCN 
21565
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 ). Overall, the SED shows a blue continuum in the NIR to optical 
region, reaching a peak around the g band and rapidly decreasing in the 
UV as constrained by the Swift/UVOT measurements (Evans et al., GCN 
21550
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 ). The spectral slope in the UV is quite steep, being well 
represented by an exponential tail or a very steep power law (spectral 
index ~3.7 on Aug 18.16 UT; and ~ 5 on Aug 18.57 UT).

A blackbody with T ~ 8500 K broadly represents the available data at a 
mean epoch Aug 18.1 UT (black line in the plot). Assuming an isotropic, 
spherically symmetric emitter, the radius of the blackbody source would 
be approximately 10^15 cm for a distance of 40 Mpc. At 55 ks after the 
explosion, this would imply a relativistic expansion velocity. As noted 
by Cenko et al. (GCN 21572
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 ), the later Swft/UVOT measurement indicate 
cooling in the source, implying further expansion and confirming the 
relativistic velocity.

The SED is clearly atypical for optical afterglows of long and short 
GRBs, as also highlighted by the lack of detection in the X-ray band 
(Evans et al., GCN 21550
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 ).

A plot showing the counterpart SED is posted online at:

http://www.astro.ku.dk/~malesani/GRB/170817A/SED_opt.png

Data were grouped in quasi-simultaneous sets and were collected from the 
following reports:
- Aug 18.0 UT (red triangles): Yang et al. (GCN 21531
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 ); Nicholl et al. 
(GCN 21541
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 ); Tanvir & Levan (GCN 21544
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 ); Simon et al. (GCN 21551
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 ); 
Singer et al. (GCN 21552
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 );
- Aug 18.16 UT (blue circles): Evans et al. (GCN 21550
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 );
- Aug 18.42 UT (green squares): Wolf et al. (GCN 21560
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 );
- Aug 18.57 UT (cyan diamonds): Cenko et al. (GCN 21572
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 ).

N. R. Tanvir (U. Leicester), A. J. Levan, D. Steeghs (U. Warwick) report:

We note that the field of NGC 4993 was observed as part
of the VISTA Hemisphere Survey on 9 April 2014.  No source
is visible at the location of the candidate counterpart 
(Coulter et al. LVC GCN 21529
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 ).  We obtain a 3-sigma upper 
limit of J(AB)=21.6, significantly fainter than the provisional magnitude
of J(AB)=17.5+/-0.1 reported for the infrared transient 
(Tanvir et al. LVC GCN 21544
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 ).

S. Eikenberry, K.Ackley, and S. Klimenko (U. Florida) report:

We have investigated archival 2MASS (28 Apr 1998) and Spitzer (12 Oct
2014) infrared observations of the field of SSS17a (Coulter et al. LVC GCN
21529
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 ). We find no evidence of a point-like source at this location. While
the presence of the host galaxy somewhat complicates sensitivity
estimates, in the case of 2MASS we have a preliminary estimate for a
3-sigma upper limit of J(Vega) ~ 17.6 +- 0.2 mag, which corresponds to
J(AB) ~ 18.5 +- 0.2 mag. This is a factor of ~2.5 fainter than the
J(AB)=17.5 mag detection of Tanvir et al. (LVC GCN 21544
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 ), indicating a
variable or transient nature for this source. More detailed analyses of
the upper limits for both 2MASS and Spitzer are forthcoming.

[GCN OPS NOTE(18aug17):  Per submitter's and author's request, the submitter
was changed from Singer to Eikenberry.  Singer submitted as Eikeberry's proxy,
because Eikenberry's GCN account was not yet activated.]

D. Kaplan (UWM), T. Murphy (University of Sydney), K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Dobie (University of Sydney) on behalf of the VAST collaboration.

Following Bannister et al. (LVC GCN 21559
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 ), who reported ATCA detections of a radio source consistent with the position of NGC 4993 that is also seen with the VLA (Alexander et al. LVC GCN 21548
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 ), we present upper limits to the radio emission of any source at the position of the potential optical counterpart, SSS17a (Coulter et al., LVC GCN 21529
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 ).

We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.706, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog).  The flux densities were consistent with the values reported by Bannister et al. (LVC GCN 21559
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 ).  We then measured the rms noise at the position of SSS17a as well as 3 other source-free positions nearby.  In all cases there was no detectable emission at the position of SSS17a (9.9 arcsec away), and the noise was essentially identical across all positions.  

Assuming that all of the emission originates with the center of NGC 4993, our flux density for the galaxy and 3-sigma upper limits to emission at the position of SSS17a are:

Frequency	NGC 4993 Flux Density	3-sigma Limit for SSS17a
8.5 GHz: 	0.66 mJy			120 uJy
10.5 GHz:	0.54 mJy			150 uJy
16.7 GHz: 	0.42 mJy			130 uJy
21.2 GHz: 	0.34 mJy			140 uJy

Thank you to CSIRO staff for supporting these observations.

S. B. Cenko (NASA/GSFC), S.W.K. Emery (UCL-MSSL), S. Campana (INAF-OAB),��P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.A. Breeveld (UCL-MSSL), E. Troja��(NASA/GSFC/UMCP), P.T. O'Brien (U. Leicester), S.D. Barthelmy��(NASA/GSFC), A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),��V.D'Elia(ASDC), P. Giommi (ASI), C. Gronwall��(PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien��(GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A.��Nousek (PSU), S.R. Oates (U. Warwick), J.P. Osborne (U. Leicester), C.��Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M.��Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),��M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report��on behalf of the Swift team:��

We obtained a second epoch of UV and X-ray imaging of SSS17a (Coulter et al.; GCN 21529
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 ), the candidate optical counterpart of G298048 (LVC; GCN 21509
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 ) with the Swift Gamma-Ray Burst Explorer.  Observations began��at 13:30 UT��on 2017��August 18.  Compared with our previous epoch of imaging (Evans et al.; GCN 21550
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 ), the source has faded significantly at UV wavelengths.  Specifically we measure the following magnitudes (with no host subtraction):

Filter T_start(s) T_stop(s) Exp(s) Mag (Vega)��

u��   90029 90164  133��17.42 +/- 0.09��
uvw1��89755 90024  265��18.50 +/- 0.15��
uvm2��89346 94665 1045��20.40 +/- 0.27��
uvw2��90170 90674  496��20.37 +/- 0.32��

Given the relatively flat evolution in the optical and NIR, this suggests significant cooling in the source.

The source remains undetected in the X-rays, with comparable limits to our previous epoch.

Further observations are planned.

P. K. G. Williams (Harvard), K. D. Alexander (Harvard), and E. Berger
(Harvard) report on behalf of a larger collaboration:

We investigated observations of the candidate optical counterpart to
LIGO/Virgo trigger G298048 in the NRAO Very Large Array (VLA) data archive.
The field containing the candidate was observed at both 1.51 GHz ("L band")
and 4.89 GHz ("C band") on June 10 and 23, 1984, as part of program AW0110.
The on-source integration times were 11.5 and 5.5 minutes, respectively. We
obtained images generated by the NRAO's VLA/AIPS data calibration pipeline
(L. Sjouwerman, in preparation), which automatically processed the data in
2009.

We see no persuasive evidence for radio emission at the location of either
the host galaxy or the counterpart candidates. We measure image RMS values
of ~180 and ~340 microJy near the candidates in the 1.51 and 4.89 GHz
images, respectively. Taking a flux density upper limit of three times the
RMS and a luminosity distance of 39.5 Mpc, these values correspond to upper
limits on the spectral luminosity of 10^27.0 and 10^27.3 erg/s/Hz at 1.51
and 4.89 GHz. Using the relation between synchrotron emission and star
formation rate presented by Yun & Carilli (2002 ApJ 568 88), the implied
star formation rate of the candidate host galaxy is less than 0.05 solar
masses per year.

For comparison, Alexander et al. (LVC GCNs 21545
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 , 21548
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 ) report a VLA
radio detection
of 300 microJy at 9.77 GHz, and Bannister et al. (LVC GCN 21559
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 ) report
ATCA radio detections of 600-400 microJy at 8.5--21.2 GHz. These values are
consistent with the archival limits.

V.M.  Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, 
P.Balanutsa,  O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov
Lomonosov Moscow State University, Sternberg Astronomical Institute

R.Podesta, C.Lopez, F. Podesta
Observatorio Astronomico Felix Aguilar (OAFA) , National University of San
Juan, Argentina

H. Levato, C. Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina

N.M. Budnev, O. Gress, K. Ivanov, S.Yazev
Irkutsk State University

V.Yurkov, Yu.Sergienko, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

D.Buckley, S. Potter, M. Kotze,
South African Astronomical Observatory

R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu
The Instituto de Astrofisica de Canarias

A. Tlatov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

As we reported in LVC GCN 21546
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  MASTER-OAFA have imaged the BAYESTAR 
localization
map of LIGO/Virgo G298048 (GCN 21513
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 ).

MASTER-SAAO  have new images of  NGC 4993 galaxy starting 2017-08-18 
17:06:55 UT in B, R and unfiletred with magnitude limit 19.8. We see
object in B and unfiltered images detected by Coulter et al. (LVC GCN  21529
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 ),
Allam et  al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 ), 
Melandri et al. (LVC GCN 21532
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 ), Lipunov et al., (LVC GCN 21546
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 ).

The OT is not essentially changed during last ~24 hours.

This message can be citted.

L. P. Singer (NASA/GSFC) reports on behalf of the Global Relay of
Observatories Watching Transients Happen (GROWTH) collaboration:

In GCN 21552
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 , our acknowledgement of the Gemini-South staff was
incomplete. We additionally thank the following Gemini staff: the
telescope operator was Ariel Lopez, the observers were Karleyne Silva and
Gonzalo Diaz, and the queue coordinator for this week and the contact
scientist for our program is Hwihyun Kim.

I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration

In GCN 21511
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  (an update to GCN 21508
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 ) we reported the identification of a neutrino candidate coincident with preliminary LIGO GW skymaps using only LHO data (GCN 21509
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 ), and Fermi GBM's preliminary skymaps (GCN 21506
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 ). This neutrino candidate is *not in the 90% credible region of the latest GW skymap* incorporating LHO, LLO, and Virgo data (GCN 21513
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 ).

The updated joint GW/High Energy Neutrino skymap is available on GraceDB at <https://gracedb.ligo.org/apiweb/events/G298048/files/coinc_skymap_initial_icecube.png,2>. A JSON-formatted list of the temporally coincident neutrinos included in the joint plot is available at <https://gracedb.ligo.org/apiweb/events/G298048/files/IceCubeNeutrinoList.json,0>.

D. A. Coulter, C. D. Kilpatrick, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, and A. L. Piro (Carnegie)

on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration:

We report a correction to the photometric magnitude of SSS17a announced in LVC GCN 21529
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 .  After re-examination of the imaging and using 97 APASS i' standards for relative photometry, we conclude that the source had a brightness of i = 17.3 +/- 0.1 mag at the time of observation on UT 2017-08-17.98.  We apologize for the error.

M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim (KASI) on behalf of the
KU collaboration



We analyzed the medium-band data we took for SSS17a at the Siding Spring
Observatory at 2017-08-18.4 (UT) in Im et al. (LVC GCN 21563
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 ). The
preliminary magnitude at the medium-band filter m475 centered at 475nm
(Choi & Im JKAS, 50, 71) is m475 = 17.5 +- 0.2 AB mag, somewhat brighter
than g ~ 17.9 mag of Wolf et al. (LVC GCN 21560
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 ) taken at the same site at
a similar time. Considering that m475 is similar to the g-band filter, this
prefers a moderate dimming in comparison to g=17.2 +- 0.1 mag at the time
of 2017-08-18.1 (UT) from Simon et al. (LVC GCN 21551
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 ) to a brightening as
suggested by Arcavi et al. (LVC GCN 21565
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 ). However, currently, the large
uncertainties in the magnitude estimates (mostly due to host galaxy
subtraction problem) makes us difficult to rule out no brightening or even
a slight brightening of the EM counterpart candidate.

I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las
Cumbres Obs), M. Zalzman, D. Poznanski (TAU), L.P. Singer (NASA/GSFC), S.
Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley), W.
Fong (Northwestern) and D. Maoz (TAU) report the brightening of SSS17a /
DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC
GCN 21529
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 ), Allam et al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 ),
Melandri et al. (LVC GCN 21532
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 ) and others.

In the course of Las Cumbres Observatory LIGO followup we observed NGC 4993
from our 1-meter telescopes at the Cerro Tololo Inter-American Observatory
in Chile at 2017-08-18 00:15 UT (Arcavi et al.; LCV GCN 21538
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 ) and at the
Siding Spring Observatory in Australia at 2017-08-18 09:10 UT. Both images
were taken in the broad w (=g+r+i) filter.

Preliminary aperture photometry, comparing to 7 nearby stars, indicates a
relative increase in brightness of the candidate by 0.11 magnitudes (with
an uncertainty of 0.03 magnitudes) in the ~9 hours between the first and
second epochs.

Further observations and analysis are ongoing.

A. Bulgarelli (INAF/IASF-Bo), M. Tavani (INAF/IAPS, and Univ. Roma Tor
Vergata), F. Verrecchia (SSDC and INAF/OAR), M. Cardillo, G. Piano
(INAF/IAPS),  M. Pilia (INAF/OA-Cagliari), C. Pittori (SSDC and INAF/OAR),
I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi,
G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and
INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo),
A. Trois (INAF/OA-Cagliari), M. Marisaldi (INAF/IASF-Bo and Bergen University),
A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:

As reported in previous GCNs of the AGILE Team (LVC GCN 21525
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  and 21526
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 )
at the G298048 event time T0 the 90% localization region (LR) of the HLV
skymap was not accessible to AGILE detectors because of a prolonged Earth
occultation of that portion of the sky.

AGILE is currently spinning and is scanning about 80% of the entire sky
every 7 minutes. The G298048 HLV LR was exposed before and after T0 with a
complex pattern that depends on the instrument boresight revolution and Earth
occultation.

In the analysis results reported below, we use the updated G298048 sky map
(LVC GCN 21527
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 ) including the optical transient SSS17a (RA = 13:09:48.09
DECL. = -23:22:53.35, Coulter et al. 2017; LVC GCN 21529
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 ) which is
the potential optical counterpart (see also Allam et al. LVC GCN 21530
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 ,
Yang et al. LVC GCN 21531
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 , Melandri et al. LVC GCN 21532
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 ) to G298048.

The closest in time AGILE-GRID detector exposure of the G298048 LR
starts near T0+950 sec. For an integration time ranging from T0+950 to
T0+1100 sec, we obtained the 3-sigma gamma-ray flux upper limit
UL_1 = 5.7e-08 erg cm^2 s^-1 at energies above 100 MeV at the optical
transient location.

Previously, the closest in time passage of the AGILE-GRID instrument over
the LR occurred at times from T0-1950 to T0-1750 sec before T0. For this
exposure we obtained the 3-sigma gamma-ray flux upper limit UL_2 = 3.4e-08
erg cm^2 s^-1 at energies above 100 MeV at the optical transient location.

We also carried out an analysis on longer timescales. For an integration
time during a 10 ksec time window preceding T0, we obtain an AGILE-GRID
gamma-ray flux upper limit of UL_3 = 2.8e-09 erg cm^-2 s^-1
at the optical transient location at energies above 100 MeV.
For an integration time of 10 ksec following T0, we obtain UL_4 = 3.5e-09
erg cm^-2 s^-1 at energies above 100 MeV at the optical transient location.

No significant new sources were found in our analysis. Additional analysis
of AGILE data is ongoing.

M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim (KASI) on behalf of the
KU collaboration

We imaged SSS17a in NGC 4993 (Coutler et al. LVC GCNs 21529
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 ), the potential
optical counterpart of LIGO/Virgo G298048 (LVC GCNs 210505
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 , 21509
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 , 21513
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 )
with the g, r, i, z and an array of medium-band filters. The observation
was carried out using two 0.43m telescopes, LSGT and T17 of iTelescope.Net
at the Siding Spring Observatory (Im et al. 2015, JKAS, 48, 207). The
observation started at 2017-08-18 09:47 (UT), and continued for about 30
min until the weather stopped the osbservation. SSS17a is clearly visible
in the images taken. Further analysis of the data is ongoing. Additional
observations are ongoing/planned using these telescopes and the KMTNet 1.5m
telescopes in the coming nights.

K. Bannister (CSIRO), R. Shannon (CSIRO/Curtin/ICRAR), A. Hotan
(CSIRO), C. James (Curtin), J-P Macquart(Curtin/ICRAR), S. Oslowski
(Swinburne), W. Farah (Swinburne) on behalf of the ASKAP
collaboration.


We observed the 90% containment region of the Bayestar map (Singer et
al. LVC GCN 21513
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 ) with 7 antennas of the The Australian Square
Kilometer Array Pathfinder (ASKAP). We recorded fast autocorrelation
data with 336 x 1 MHz channels and a time sampling of 1.26 ms centered
at 1320 MHz (see [1] for observing details). We used flys-eye
observing mode, with some parts of the field covered by 2 antennas and
some by 1 antenna.

We had 2 observing runs starting roughly 16h after the gravitational
wave trigger:

Run 1: 2017-08-18 04:05:35 to 2017-08-18 07:44:56 UT

Run 2: 2017-08-18 08:57:33 to 2017-08-18 13:02:20 UT

We are searching the data for fast radio bursts.


[1] Bannister et al. 2017, ApJL, 841, 12



-- 
Keith Bannister

Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Furusawa, H.,
Koshida, S. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima Univ.),
Tominaga, N. (Konan Univ.), Motohara, K., Ohsawa, R., Morokuma, T.,
Yasuda, N. (Univ. of Tokyo), Kawai, N. (Tokyo Tech) on behalf of
the J-GEM collaboration

As reported in Yoshida et al. 2017 (GCN 21549
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 ), we performed z-band imaging
observations for the gravitational wave event G298048 (GCN 21505
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 ; 21509; 21513)
with Hyper Suprime-Cam attached to the Subaru telescope on August 18 2017 UT. 
The survey fields include SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, 
Coulter et al. 2017; GCN 21529
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 ) possibly associated with G298048. After photometric
calibration with Pan-STARRS1 catalog (Chambers et al. 2016) using HSC
pipeline (Bosch et al. 2017), we obtained psf magnitude of z = 17.3, which 
is consistent with the magnitudes reported by Chambers et al. (GCN 21553
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 ). 
We did not find a significant variability with > 0.1 mag during
our observations from 5:16 UT until 5:40 UT.

C. Wolf, S.W. Chang, A. M�ller (ANU)

We report photometry of the optical source in NGC 4993 reported by Coulter et al. (LVC GCN 21529
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 ), Allam et al. (LVC GCN 21530
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 ), Yang et al. (LVC GCN 21531
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 ), Melandri et al. (LVC GCN 21532
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 ) in response to LIGO/Virgo GW trigger G298048 (LVC, GCN 21513
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 ).

The source at  RA = 13:09:48.09 DECL. = -23:22:53.35 was observed with the 1.35-m ANU SkyMapper telescope at Siding Spring Observatory on the night of 2017-08-18 from 10:00:00 to 10:09:40 UTC.

Initial photometry for the candidate�s AB magnitude is: u-band (350/40) = 17.9 +/- 0.15, v-band (384/28) = 17.9 +/- 0.10, g-band (510/156) = 17.76 +/-0.05, r-band (617/156) = 17.20 +/-0.05 and i-band (779/140) = 16.0 +/- 0.30. Note that the u-band is uncertain because the frames were taken at airmass 2.5 to 2.7, and the i-band is highly uncertain due to a rudimentary host subtraction.

K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Kaplan (UWM),
T. Murphy (University of Sydney), D. Dobie (University of Sydney) on behalf
of the VAST collaboration.

We observed 54 candidate host galaxies in the LIGO/Virgo
G298048 localisation volume with the Australia Telescope Compact Array
(LVC GCN 21513
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 , sky map; LVC GCN 21519
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 , 54
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  nearby galaxies).
Observations started at 2017-08-18 01:00 UT and ended at
2017-08-18 09:14:15 UT with approximately 1-2 minutes of on-source
time for each target.

We detect an unresolved radio source coincident with NGC 4993. The
best-measured position was at 8.5 GHz:

RA = 13:09:47.7
Dec = -23:22:59.1

(J2000) with positional errors of 1��� in RA and 4��� in declination.

This position is in agreement with the VLA detection of a radio source
(Alexander et al. LVC GCN 21548
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 ) within the stated errors of each observation.

We report preliminary flux densities of:

~0.6 mJy at 8.5 GHz
~0.5 mJy at 10.5 GHz
~0.4 mJy at 16.7 GHz
~0.4 mJy at 21.2 GHz

We find no evidence for any radio emission at the position of the optical
transient (Coulter et al. LVC GCN 21529
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 ).

Analysis of the full dataset is underway. Subsequent epochs are planned.

Thank you to CSIRO staff for supporting these observations.


-- 
Keith Bannister

A. Klotz (IRAP CNRS/UPS), R. Laugier, M. Boer, K. Noysena (ARTEMIS 
CNRS/UCA/OCA) report on behalf of the TZAC collaboration

We have observed the initial error box with the TRE (TAROT-Reunion) 
Telescope located at Les Makes Observatory, La R��union Island, France. 
Each image (no filter)  lasts for 120s and covers a field of 4.2 x 4.2 
deg2, with a magnitude limit of 17.0. Unfortunately the position of the 
candidate afterglow reported by Coulter et al. (LVC GCN 21529
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 ) was not 
in the position observable at that time given the automated generation 
of the fields, the mixed weather conditions, and the position of the GW 
candidate transient in the sky.

We list below the log of the observations. Images are under analysis.

Date                                    RA            DEC

2017-08-17T17:48:54    220.121 -43.833
2017-08-17T17:51:01    220.119 -43.832
2017-08-17T18:20:39    228.450 -48.036
2017-08-17T18:22:46    228.448 -48.035

2017-08-17T18:25:02    219.216 -52.230
2017-08-17T18:27:09    219.213 -52.228
2017-08-17T18:29:16    219.212 -52.226

2017-08-17T22:06:59     32.142 +40.179
2017-08-17T22:09:06     31.598 +40.180
2017-08-17T22:11:14     31.087 +40.183

2017-08-17T22:36:21     34.642 +42.385

2017-08-17T22:38:28     36.473 +40.141
2017-08-18T00:29:44     41.936 +40.144
2017-08-18T00:31:50     41.938 +40.143
2017-08-18T01:18:34     41.901 +40.145
2017-08-18T01:20:41     41.903 +40.145

2017-08-18T00:33:59     30.905 +40.147
2017-08-18T00:36:06     30.907 +40.147
2017-08-18T00:38:14     30.909 +40.147
2017-08-18T01:22:57     30.870 +40.151
2017-08-18T01:25:04     30.872 +40.151
2017-08-18T01:27:11     30.874 +40.151

2017-08-18T01:05:32     36.396 +40.145
2017-08-18T01:07:39     36.398 +40.145
2017-08-18T01:52:20     36.369 +40.149
2017-08-18T01:54:27     36.371 +40.150
2017-08-18T01:56:34     36.373 +40.151

R. J. Foley (UC Santa Cruz) reports

In the interest of focusing follow-up observing resources, we perform a quick assessment of how ���unique��� the potential EM counterpart to the LIGO/Virgo G298048 trigger (LVC GCNs 21509
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 , 21513
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 ), SSS17a (Coulter et al., LVC GCN 21529
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 ), is in the context of other extragalactic astrophysical transients.

The optical spectrum (Drout et al., LVC GCN 21547
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 ) and colors (Nicholl et al., LVC GCN 21541
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 ; Chambers et al., LVC GCN 21553
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 ) are inconsistent with a Type Ia supernova at any epoch.  Its nominal host galaxy, NGC 4993, is an S0 galaxy, which typically have little star formation (although there are dust lanes near the SN position; Foley et al., LVC GCN 21536
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 ).  If at the distance of its nominal host galaxy, NGC 4993, correcting for only Milky Way extinction, SSS17a had a peak luminosity of M_g ~ -16.0 mag (e.g., Simon et al., LVC GCN 21551
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 ), which is much more luminous than novae, much less luminous than SNe Ia near peak, and similar to some core-collapse SNe near peak.  The lack of a strong source in recent imaging (Cowperthwaite et al., LVC GCN 21533
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 ) indicates that SSS17a is <~ 2 days old.  At the very least, there was no source to deep limits from Hubble images ~4 months ago (Foley et al., LVC GCN 21536
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 ).  These data provide strongly constraining information on the nature of SSS17a.

Approximately 7.3% of all supernovae in S0 galaxies are core-collapse galaxies (Foley & Mandell, 2013, ApJ, 778, 167).  Using the luminosity of NGC 4993 and the formulae of Li et al. (2011, MNRAS, 412, 1473), we find that ~17% of all supernovae in S0 galaxies with a similar luminosity to that of NGC 4993 are core-collapse SNe.

Using the Li et al. local volumetric core-collapse rate, we expect ~0.1 core-collapse SN per year in the 90% LIGO localization volume.  A core-collapse SN exploding within 2 days of the LIGO trigger and within this volume has a probability of roughly 5 x 10^-5.  Including all SNe, this number only increases to 8 x 10^-5.  The probability of a core-collapse SN exploding since the Hubble images were obtained inside the LIGO volume is ~0.003.  We note that these calculations do not account for possible overdensities, and NGC 4993 is a member of a relatively massive group of galaxies.

Finally, examining the core-collapse luminosity functions of Li et al. (2011, MNRAS, 412, 1441), ~50% of Type Ib/c supernovae and ~65% of Type II supernovae in S0-Sbc galaxies have peak absolute magnitudes greater than -16.0 mag.  That is, roughly half of all core-collapse SNe in S0-Sbc galaxies never reach the reported magnitude of SSS17a.

Combined, we estimate that the likelihood of SSS17a being an unrelated core-collapse SN in NGC 4993 to be ~5 x 10^-6.  Excluding the strongest constraints related to possible recent non-detections, the likelihood of SSS17a being an unrelated core-collapse SN in NGC 4993 is ~3 x 10^-4.

We conclude that SSS17a is a rare event, and warrants significant additional follow-up observations.

A. Melandri, P. D'Avanzo, S. Campana, S. Covino (INAF-OAB), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report:


We carried out optical/NIR follow-up observations of the LIGO/Virgo GW trigger G298048 (LVC GCN Circ. 21509
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 , 21513
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 ) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile) by performing targeted observations of catalogued galaxies in the LVC skymap. The observations were carried out from 23:11:29 UT on 2017 Aug 17 (i.e. 10.5 hours after the event detection) to 02:08:24 UT on on 2017 Aug 18, simultaneously in the g, r, i, z and H bands. 

We observed 18 galaxies (see table below). Group1 targets were selected within 3sigma from the position of the neutrino candidate reported in LVC GCN Circ. 21511
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 , with a distance consistent with the GW trigger; Group2 targets are a sub-sample of the galaxies within the 50% probability region reported in the LVC GCN Circ. 21516
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 ; Group3 targets are galaxies reported in LVC GCN Circ. 21519
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 , 21521
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 .

  RA(J2000)      Dec(J2000)    Distance (Mpc)    

---Group1
12:04:20.16	-01:31:49.58   27.41	
12:01:11.04	-01:17:43.30   28.19	
12:13:38.88	-01:17:36.56   34.27	
12:02:31.68	-02:18:11.52   40.08 	
12:16:44.16	-02:48:37.08   45.95 	
12:06:52.80	-04:02:36.96   26.25
12:00:24.96	-04:54:49.32   35.73 *
---------------------------------------
---Group2
12:57:27.90     -19:41:28.67   44.75 
13:07:33.75     -24:00:30.98   43.94 
13:08:04.32     -23:47:48.64   34.09 
13:06:56.51     -23:55:01.45   33.65 
13:07:05.97     -23:40:37.34   33.42 
13:07:37.73     -23:34:44.11   41.75 
13:06:24.01     -24:09:50.42   33.43 
13:07:37.68     -23:56:18.11   45.98 
13:06:19.39     -22:58:49.18   39.36 
---------------------------------------
---Group3
13:09:47.68     -23:23:02.03   41.66
13:16:23.25     -26:33:41.03   45.59

*: we detected a possible optical source in this field at the following coordinates: RA(J2000),Dec(J2000) = 12:00:26.76,-04:55:04.2 (+/- 0.5"). This source is faint, having a magnitude of r~19.3 (i.e. close to the limiting magnitude of our observations) and we cannot establish the nature of this objects. However, its position seems to be consistent (within 3 arcmin) with a minor planet (23444-Kukucin). 

A preliminary analysis (also based on visual comparison with the DSS) reveals no obvious optical/NIR candidate counterpart in the above galaxies down to the following magnitudes: r > 19.5, H > 17.0 (AB, 3sigma UL).