LIGO/Virgo G288732

The LIGO Scientific Collaboration and Virgo Collaboration report:

The PyCBC binary-merger search (Nitz et al., arXiv:1705.01513
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 ; Usman
et al. 2016, CQG 33, 215004) identified candidate G288732 in analysis
of data from the LIGO Livingston Observatory (L1) at 2017-06-08
02:01:16.492 UTC (GPS time: 1180922494.492). This circular was delayed
as the LIGO Hanford detector was not in observing mode at this time
and manual investigations were required.

The Livingston detector was operating nominally at the time of the
trigger, however the Hanford detector was undergoing a period of
active commissioning at the time of the trigger. The trigger was first
identified by inspection of PyCBC triggers from the Livingston
data. Manual follow-up of the Hanford data identified a coincident
trigger with consistent parameters.  The Virgo detector was locked but
in a commissioning mode at the time; Virgo data has not yet been used
in this analysis. Offline analysis is ongoing.

Commissioning activities were ongoing for two minutes around the time
of the trigger, but studies suggest this activity only affected
frequencies below 30 Hz. This is below the starting frequency of the
manual re-analysis. Other than the Hanford activity below 30 Hz, the
state and calibration of the detectors appears nominal.

Due to the Hanford commissioning activities, the amount of data
available to estimate the noise background was limited to
approximately 15 minutes. Using these data, we estimate that the false
alarm rate of G288732 is less than (i.e. more significant than) 2.6
per year, however the signal-to-noise ratio of this candidate is
consistent with a higher significance.

The event's properties can be found at this URL:
https://gracedb.ligo.org/events/G288732

If G288732 is astrophysical, it is likely to be a binary black hole
merger.

The gstlal binary-merger search (Messick et al., 2016, PRD 95, 042001)
identified a consistent trigger in the Livingston data at the time of
the candidate.

One sky map with distance information (e.g., Singer et al. 2016, ApJL 829,
15) is available at this time and can be retrieved from the GraceDB event
page: bayestar.fits.gz, an initial localization generated by the BAYESTAR
pipeline. The 50% credible region spans about 230 deg2 and the 90% region
about 860 deg2. The luminosity distance is 320 +/- 100 Mpc (all-sky mean
+/- standard deviation). This is the preferred sky map at this time.

We caution that the parameters of this candidate may be subject to change
as data-quality and calibration studies are ongoing.

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:

  Using on-line data from the ANTARES detector, we have performed a
  follow-up analysis of the recently reported LIGO/Virgo G288732 event
  using the initial LIGO Bayestar probability map at event time (LVC
  GCN Circ. 21221
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 ). The ANTARES visibility 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/G288732/G288732.png (gwantares/
  ANT@GW28). Considering the location probability provided by the LIGO
  collaboration, there is a 55% chance that the GW emitter was in the
  ANTARES field of view.

  No up-going muon neutrino candidate events were recorded within the 90%
  contour during a +/- 500s time-window centered on the G288732 event
  time. The expected number of atmospheric background events in the
  region visible by ANTARES is ~2.4e-2 in the +/- 500s time window. An
  extended search during +/- 1 hour gives no up-going neutrino
  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.  In the range 1-100 TeV, ANTARES has the best sensitivity to a
  large fraction of the Southern sky.

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

In response to the LIGO/Virgo GW event G288732 at T0 = 2017-06-08
02:01:16.492 UTC, a preliminary analysis of the AGILE MiniCALorimeter
(MCAL)
data found no event candidates within a time interval covering
approximately
-/+ 10 sec from the LIGO T0.

3-sigma ULs were computed for a 1 s integration time on different celestial
positions within the G288732 error region, for a typical value of the
fluence
of 6.4e-7 erg cm^-2 (assuming as spectral model a power law with photon
index
1.4). The AGILE-MCAL detector is a CsI detector with a 4-pi FoV, working in
the range 0.4 - 100 MeV.  Additional analysis of AGILE data is in progress.

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


We previously reported on the online track-like neutrino search for LIGO-Virgo trigger G288732. We are updating this result with adopting a new online configuration, which enables better background rejection online, allowing for an increased rate of events passing the neutrino track event selection, along a higher efficiency for neutrino events. With this online search, the expected background neutrino rate is ~6 within our [-500,500] time window.

----

We searched IceCube online track-like neutrino candidates (GFU) detected in a [-500,500] second interval about the LIGO-Virgo trigger G288732. We compared the candidate source directions of 7 temporally-coincident neutrinos to the BAYESTAR skymap, with the following parameters:

#            dt[s]     RA[deg]    Dec[deg]      E[TeV]  Sigma[deg]
------------------------------------------------------------------
1.         -106.97        28.5        23.7        1.03         1.2
2.          -97.96       252.1         8.0        0.90         1.8
3.          -67.26       299.0        28.6        1.38         1.4
4.          -44.07        99.0       -67.8      224.91         0.2
5.          331.13       269.8        43.7        1.09         5.7
6.          337.70       241.7        26.3        0.97         1.5
7.          462.61       310.9        -5.5        2.53         0.8


(dt--time from GW in [seconds]; RA/Dec--sky location in [degrees]; E--reconstructed secondary muon energy in [TeV]; Sigma--uncertainty of direction reconstruction in [degrees])

The analysis found NO COINCIDENT ONLINE TRACK-LIKE NEUTRINO CANDIDATES detected by IceCube within the 500 second window surrounding G288732 within the BAYESTAR skymap.

A coincident neutrino-GW skymap has been posted to GraceDB (<https://gracedb.ligo.org/apiweb/events/G288732/files/coinc_skymap_initial_icecube.png,2>). A JSON-formatted list of the above neutrinos can be downloaded from GraceDB at:<https://gracedb.ligo.org/apiweb/events/G288732/files/IceCubeNeutrinoList.json,3>

In addition, we are performing coincident searches with other IceCube data streams, including the high-energy starting events (HESE) and Supernova triggers.  HESE events have typical energies > 60 TeV and start inside the detector volume, leading to a relatively pure event sample with a high fraction of astrophysical neutrinos.  The SN trigger system is sensitive to sudden increases in photomultiplier counts across the detector, which could indicate a burst of MeV neutrinos.  We will submit separate GCN circulars if coincident HESE or SN triggers are found.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica.  For a description of the IceCube realtime alert system, please refer to<http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1610.01814
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 >; for more information on joint neutrino and gravitational wave searches, please refer to<http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1602.05411
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 >.

Nicola Omodei (Stanford), Daniel Kocevski (NASA/MSFC), Giacomo Vianello (Stanford), Judith Racusin, Sara Buson, Jeremy S. Perkins and Julie McEnery (NASA/GSFC) 
report on behalf of the Fermi-LAT team:

We have searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger G288732.
At the time of the trigger (T0 =  2017-06-08 02:01:16.492 UTC, 518580081.492 MET), none of the LIGO Bayestar probability map was in the LAT field of view. Part of the region entered the LAT field of view 70 seconds after T0, and we reached 100% cumulative coverage within ~6.5 ks after the trigger. We define "instantaneous coverage" as the integral over the region of the LIGO probability map that is within the LAT field of view at a given time, and "cumulative coverage" as the integral of the instantaneous coverage over time. 
We performed a search for a transient counterpart within the 90% contour of the LIGO map in the time window from T0  to T0 + 10 ks, and no significant new sources are found above a Test Statistic (TS) of 25. 
On this time scale, the highest significance excess found was at R.A.,Dec.=128.11, 43.39, (J2000) with a localization error of 0.24 degrees (90% c.l.), with a TS of 23, corresponding to a pre-trial significance of 4.8 sigma. Given the number of trials involved, the post trial significance of this excess is estimated to be ~3.5 sigma.  The location of the candidate was occulted by the Earth at the time of the LIGO trigger, and came into the FoV at ~1200 s after T0.
A Swift ToO observation has been requested to initiate follow-up observations at the location of this candidate source and we encourage additional follow-up observations.

The Fermi-LAT point of contact for this event is: nicola.omodei@stanford.edu

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

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

In response to the LIGO/Virgo GW trigger G288732 (GCN #21221
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 ), we performed
an analysis of the AGILE Gamma-Ray Imaging Detector (GRID) data on
different
timescales. On LIGO trigger time (T0=2017-06-08 02:01:16.492 UTC) the GRID
exposure covered approximately 40% of the LIGO localization region observed
with off-axis angles between 40 and 70 deg.

An analysis of the data in the energy range 50 MeV - 10 GeV was performed
on timescales from 2 to 100 sec centered at T0.
Preliminary values of 3-sigma upper limits (UL) obtained within the
accessible G288732 localization region are reported below:

from 1.6e-06 to 3.1e-06 erg cm^-2 s^-1 for integration time of 2s
from 1.6e-07 to 6.8e-07 erg cm^-2 s^-1 for integration time of 20s
from 4.0e-08 to 3.0e-07 erg cm^-2 s^-1 for integration time of 100s

These ULs apply to a large fraction of the GRID-exposed LIGO localization
region.

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

N. Leroy (LAL), X.H. Han (NAOC), S. Antier (LAL), J.Y. Wei (NAOC),
C. Wu (NAOC), L.P. Xin (NAOC), X.M. Meng (NAOC), L. Huang (NAOC),
Y. Xu (NAOC), H.B. Cai (NAOC), J. Wang (NAOC), X.M. Lu (NAOC),
Y.L. Qiu (NAOC), J.S. Deng (NAOC), L. Cao (NAOC), S. Wang (NAOC),
L. Jia (NAOC), S.C. Zou (NAOC), S.F. Liu (NAOC), Q.C. Feng (NAOC),
H.L. Li (NAOC), D.W. Xu (NAOC), Y.J. Xiao (NAOC), W.L. Dong (NAOC),
Y.T. Zheng (NAOC), E.W.Liang (GXU), X.G.Wang (GXU), Y.G. Yang (HBNU),
B. Cordier (CEA), S.N. Zhang (NAOC), D. Dornic (CPPM), B.B. Wu (IHEP),
D. Turpin (IRAP), A. Klotz (IRAP), C.Lachaud (APC),
on behalf of the SVOM Gravitational Astronomy group report:

We observed about 1200 square degree (3 sky regions) of the skymap
of the advanced LIGO trigger G288732, with SVOM/Mini-GWAC, at Xinglong
Observatory of NAOC equipped with U9000 camera (FOV~400 square
degree/camera).
SVOM/Mini-GWAC comprises 12 wide field angle cameras (aperture=7cm),
working with unfiltered band. The observations are operated in time-series
mode, taking one exposure in 15 seconds (10s exposure + 5s readout).
The limit magnitude is ~12 mag in R band. We estimate a 20.1% prior
probability that these 3 regions contain the true location of the
source.

The coordinates of the 3 regions and observation time are list following:

start-obs(UTC)  end-obs(UTC)    Ra      Dec     Camera_ID
2017-06-08 16:58:35 2017-06-08 19:36:46 01:15:34.8 +70:03:21   C3
2017-06-08 17:10:44 2017-06-08 19:31:01 01:22:21.1 +49:56:18   C4
2017-06-08 19:10:51 2017-06-08 19:32:59 03:56:21.7 +69:30:35   C5

The covering map is available at:
http://svom.bao.ac.cn/svomgwpub/skymap/G288732_skymap_miniGWAC.png
(svom:gw2017@svom)

The first image (which is covered in our routine survey) was taken
14 hours 57 minutes after the event trigger.
No any significant transient is found in our online pipeline. The
image analysis is ongoing in detailed processing with our offline
pipeline.

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

We investigated serendipitous INTEGRAL observations carried out at the
time of the LIGO/Virgo burst candidate G288732.  The satellite was
pointing at RA=180.649, Dec=-60.391, far from the high-probability
area of LIGO localization. Depending on the location within the LIGO
localization region, as well as the assumed counterpart spectrum and
duration, the best upper limit is set by the anti-coincidence shield
of the spectrometer on board of INTEGRAL (SPI/ACS) or by the
anti-coincidence shield of the IBIS instrument (IBIS/Veto).  The
combination of these instruments covered the full LIGO localization
region and provided constraints on the flux of a possible
electromagnetic counterpart in the energy range covered by the
INTEGRAL instruments, although the localization was somewhat
unfavorable for the INTEGRAL observation.

The INTEGRAL Burst Alert System (IBAS) did not identify any unusual
transients in coincidence with the LIGO/Virgo trigger. The IBAS
inspects both ISGRI Field of View and all-sky SPI-ACS light curve.

We investigated the SPI-ACS and IBIS/Veto light curves between -500
and +500 s from the trigger time (2017-06-08 02:01:16.5 UTC) on
temporal scales from 0.1 to 100 s, and found no evidence for any
deviation from the background.

We estimate a 3-sigma fluence upper limit enclosing 90% of LIGO
probability of 1.65e-6 erg/cm2 (75-2000 keV) for 8s duration assuming
Band model parameters alpha=-1, beta=-2.5, and E_ peak = 300 keV.

To derive a limit for a typical short burst with 1 s duration, we use
a harder cutoff power law spectrum with a photon index of -0.5 and an
Epeak = 500 keV and we find a limiting fluence of 4.3e-7 erg/cm2
(75-2000 keV) at 3 sigma c.l. This limit applies to 90% of LIGO
localization probability.

P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.D. Barthelmy
(NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL),
D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), 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), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G.
Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP) report on behalf of
the Swift team:

Swift performed a four-pointing follow up of the possible LAT source in
the error region of GW trigger G288732 (Omodei et al., LVC Circ.
21227). The observations currently span from 63 ks to 91 ks after the
LVC Trigger, and we obtained 1.4-3.9 ks per field.

We have detected 7 X-ray sources. Sources 4&5 are known X-ray emitters
(1RXS J083249.9+432322 and 1RXS J083409.3+431912 respectively). The
remaining sources are uncatalogued and have fluxes consistent with
catalogue upper limits, and show no evidence for fading. We therefore
cannot reliably associate any of these with either the possible LAT
detection or the GW event. Unfortunately, this region of the sky is now
in Swift's Sun observing constraint until September, so no further
follow up will be conducted before that time.

The automated analysis assigns each source is a rank of 1-4 which
describes how likely it is to be related to the GW trigger, with 1
being the most likely and 4 being the least likely. The ranks are
described at http://www.swift.ac.uk/ranks.php.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 4 sources of rank 3
  * 2 sources of rank 4

For all flux conversions and comparisons with catalogues and upper
limits from other missions, we assumed a power-law spectrum with
NH=3e20 cm^2, and photon index (Gamma)=1.7


RANK 3 sources
==============

These are uncatalogued X-ray sources, however they are not brighter
than previous upper limits, so do not stand out as likely counterparts
to the GW trigger.
  
  Source 1:
  =============
    RA: 	 128.2633 ( = 08h 33m 3.19s) J2000
    Dec:	 +43.2130 ( = +43d 12' 46.8") J2000
    Error:	 +8.6 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.4e-02 +/- 1.1e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 6.1e-13 +/- 4.6e-13 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 1.4e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    The source may be fading, at the 0.6-sigma level.
    There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source
    and consistent (within 3-sigma) with the distance to the GW object.

    A SIMBAD object `LEDA 2215540' is 6.4" away.
    There is 1 2MASS object within the source's 3-sigma error radius.
  
  Source 2:
  =============
    RA: 	 128.0321 ( = 08h 32m 7.70s) J2000
    Dec:	 +43.4975 ( = +43d 29' 51.0") J2000
    Error:	 +5.7 (arcsec, radius, 90% confidence).
    Peak Rate:	 3.9e-03 +/- 2.4e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 1.7e-13 +/- 1.0e-13 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 1.6e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW 

      object.
  
  Source 3:
  =============
    RA: 	 127.8821 ( = 08h 31m 31.70s) J2000
    Dec:	 +43.4300 ( = +43d 25' 48.0") J2000
    Error:	 +6.3 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.3e-02 +/- 9.7e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 5.4e-13 +/- 4.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 4.2e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    The source may be fading, at the 0.4-sigma level.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW 

      object.
  
  Source 6:
  =============
    RA: 	 128.4283 ( = 08h 33m 42.79s) J2000
    Dec:	 +43.2892 ( = +43d 17' 21.1") J2000
    Error:	 +5.0 (arcsec, radius, 90% confidence).
    Peak Rate:	 5.1e-03 +/- 2.0e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 2.2e-13 +/- 8.6e-14 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 2.1e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW 

      object.
    There is 1 2MASS object within the source's 3-sigma error radius.

 Source 7:
  =============
    RA: 	 127.8022 ( = 08h 31m 12.53s) J2000
    Dec:	 +43.4288 ( = +43d 25' 43.7") J2000
    Error:	 +7.6 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.2e-02 +/- 7.4e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 5.1e-13 +/- 3.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 3.2e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW
      object.
    There is 1 2MASS object within the source's 3-sigma error radius.

RANK 4 sources
==============

These are catalogued X-ray sources, showing no signs of outburst
compared to previous observations, so they are not likely to be related
to the GW trigger.
  
  Source 4:
  =============
    RA: 	 128.2174 ( = 08h 32m 52.18s) J2000
    Dec:	 +43.3858 ( = +43d 23' 08.9") J2000
    Error:	 +6.0 (arcsec, radius, 90% confidence).
    Peak Rate:	 8.7e-03 +/- 5.4e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 3.7e-13 +/- 2.3e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J083249.9+432322 in the ROSAT/RASSFSC catalogue
    Separation:  28.2" from the XRT source
    Cat Rate:	 1.7e-02 +/- 8.5e-03 ct/sec 
    Cat Flux:	 4.9e-13 +/- 2.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source is not above the catalogued flux.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW
      object.
  
  Source 5:
  =============
    RA: 	 128.5303 ( = 08h 34m 7.27s) J2000
    Dec:	 +43.3192 ( = +43d 19' 09.1") J2000
    Error:	 +7.2 (arcsec, radius, 90% confidence).
    Peak Rate:	 9.4e-03 +/- 5.8e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 4.0e-13 +/- 2.5e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J083409.3+431912 in the ROSAT/RASSFSC catalogue
    Separation:  22.5" from the XRT source
    Cat Rate:	 2.3e-02 +/- 1.1e-02 ct/sec 
    Cat Flux:	 6.5e-13 +/- 3.1e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source is not above the catalogued flux.
    The source may be fading, at the 0.3-sigma level.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW 

      object.

This circular is an official product of the Swift team.

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

We report the search results in the BAT data within T0 �� 100 s of the
LIGO event G288732 (LIGO/VIRGO Collaboration GCN Circ. 21221
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 ),
where T0 is the LIGO trigger time (2017-06-08T02:01:16.492 UTC).

The spacecraft was slewing from T0-95.58 s to T0+39.82 s.
The BAT pointing position at T0 is
RA = 189.362 deg,
DEC = -9.266 deg,
ROLL = 270.978 deg.
The BAT field of view (>10% partial coding) covers 0.0% of the integrated
LIGO localization probability.  That is, there is no overlap between the BAT 
field of view and the LIGO probability region at T0.

No significant detections (signal-to-noise ratio >~ 5 sigma) are found
in the BAT raw light curves with time bins of 64 ms, 1 s, and 1.6 s, respectively.
Assuming an on-axis (100% coded) short GRB with a typical spectrum in the BAT
energy range (i.e., a simple power-law model with a power-law index of -1.32;
Lien & Sakamoto et al. 2016), the 5-sigma upper limit in the 1-s binned light
curve corresponds to a flux upper limit (15-350 keV) of ~ 1.6 x 10^-7 erg/s/cm^2.
Please note that because the spacecraft was slewing during this time, the
background changes more significantly and thus this flux limit estimation is
more uncertain.

Event data exist from T0-94.683 s to T0+57.420 s. Source detections using
mosaic images (15-350 keV) with 1 s, 2 s, and 10 s intervals centered at T0
do not find any significant sources above 6 sigma.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 93.06% of the integrated LIGO
localization probability was outside of the BAT FOV but above the Earth's limb
from Swift's location, and the corresponding flux upper limits for this region
are within roughly an order of magnitude of those within the FOV.

S.W.K. Emery (UCL-MSSL), S.R. Oates (Uni. of Warwick), S.D. Barthelmy
(NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL),
D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC),
G. Cusumano(INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),
V.D'Elia(ASDC), P.A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU),
J.A. Kennea (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),
B. Mingo (U. Leicester), J.A. Nousek (PSU), 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), B. Sbarufatti
(INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja
(NASA/GSFC/UMCP) report on behalf of the Swift team:

The Swift/UVOT performed a four-pointing follow up of the possible LAT source in
the error region of GW trigger G288732 (Omodei et al., LVC Circ. 21227). The
observations currently span from 62.8 ks to 86.3 ks after the LVC trigger. We detect
optical sources in the XRT error circles of 'source 3', 'source 6' and 'source 7', but
these are also present in the SDSS catalogue and we do not find evidence of fading.
Additionally, the XRT error circle for 'source 5' is on the edge of the UVOT detector,
but we do not see any optical source in the error circle. We do not find any optical
afterglow consistent with the LAT position or 'source 1', 'source 2' and 'source 4' of
the XRT follow up of G288732 (Evans et al., GCN Circ. 21233
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 ) in the UVOT exposures
at more than 3 sigma.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the
exposures are:

XRT_source      Filter    T_start(s)  T_stop(s)  Exp(s)    Mag/3sigUL

1       u          63081           85743          1737      > 20.8
2       u          62802           85173          1764      > 20.5
4       u          62942           86261          1710      > 20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the transient
(Schlegel et al. 1998).

D. Xu (NAO/CAS), J.Z. Liu, H.B. Niu, S.G. Ma, Y. Zhang, X. Zhang, G.X. 
Pu,T.Z. Yang, F.F. Song (XAO/CAS), H.B. Zhao, B. Li, G.T. Zhaori, H. Lu, 
R.Q. Hong, L.F. Hu (PMO/CAS), H.X. Feng, Z.P. Zhu, T.M. Zhang, X. Zhou, 
H.X. Feng, Z.P. Zhu (NAO/CAS), J. Mao, J.M. Bai (YNAO/CAS) report on 
behalf of the Gravitational Wave Follow-Up Network by NAO-PMO-XAO-YNAO 
in China (GWFUNC):

We have performed tiled observations of LIGO/Virgo G288732 (LVC, GCN 
21221
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 ) using the Nanshan One-meter Wide field Telescope (NOWT) with a 
FOV of 1.3 x 1.3 deg^2, located in Xinjiang, China. Observations started 
at 18:21:44 UT and ended at 21:31:17 UT on 2017-06-08, covering a total 
area of ~337 deg^2 and with each exposure of 150s in the R-band. Data 
analysis is still underway. We note that the Fermi/LAT error circle 
(Omodei et al., GCN 21227
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 ) was not covered in the tiled observations, 
because the LAT altitude was too low since the starting of the observations.

However, the NOWT manged to image the Fermi/LAT error circle at the very 
beginning of the following night, and we obtained 3x150s and 2x200s 
R-band images around 15:30:19 UT on 2017-06-09. Five uncatalogued X-ray 
sources by Swift/XRT have been reported, which might be the X-ray 
counterpart candidates of the Fermi/LAT transient (Evans et al. GCN 
21233
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 ). These five sources, i.e., sources #1, 2, 3, 6, and 7, are within 
the FOV of each Nanshan exposure. Comparison with DSS-II, SDSS, and 
PanSTARRS reveals that sources #1, 3, 6, and 7 have known optical 
counterparts already, and no apparent strong variation in brightness for 
the optical counterparts. Source #2 doesn't have any optical counterpart 
in the DSS-II, SDSS, and PanSTARRS surveys. No optical transient is 
detected at the source #2 position in the Nanshan images, down to a 
limiting magnitude of R>19.2 mag. Therefore, deeper photometry at this 
position is encouraged.

The LIGO Scientific Collaboration and Virgo Collaboration report:

We have re-analyzed LIGO data around the time of the compact binary
coalescence (CBC) event candidate G288732 (GCN 21221
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 ) taking into
account our current understanding of calibration uncertainties.

Parameter estimation has been performed using LALInference (Veitch et
al., PRD 91, 042003) and a new sky map, LALInference.fits.gz, is
available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/events/G288732

This is the preferred sky map at this time. This map spans one arc in
the Northern hemisphere in nearly the same position as the original
BAYESTAR sky map but the region with the highest probability has
shifted further north.

The 50% and 90% credible regions span about 340 and 1090 square
degrees, respectively, which are somewhat larger than the initial
BAYESTAR sky map due to marginalizing over calibration uncertainties.

We will recalculate the sky map once the full recalibration is
complete and will share it at that time, but that is likely at least a
few weeks away.

S. Sugita, N. Kawai (Tokyo Tech), M. Serino (RIKEN), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N.Isobe (JAXA),
T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, M.
Matsuoka (RIKEN),
T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU),
H. Tsunemi, T. Yoneyama (Osaka U.),
M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.),
Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.),
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.),
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

We examined the MAXI/GSC all-sky X-ray images (2-20 keV) obtained
in the orbit and the day after the LVC trigger
G288732 at 2017-06-08 02:01:16.492 UTC (GCN 21221
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 ).

At the trigger time of G288732,
the high-voltage of MAXI/GSC was off.
One day image covers 100% of the 90% regions
in the bayestar skymap.
No significant new source was found in these images.
The upper limits for the X-ray flux are different depending
on the part of the sky.
For instance, typical 2-20 keV 1-sigma (3-sigma) upper limits obtained
from the one-day images are  3(9) mCrab.

MAXI/GSC also observed the position of the LAT counterpart
(Omodei et al., GCN 21227
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 ). The first scan after the event
was at 2017-06-08T17:39:41 (UT). No significant emission was observed
at the position at the scan. The 1-sigma (3-sigma) upper limits in 2-20 keV
are 8 (24) mCrab.

If you require information of X-ray flux by MAXI/GSC at specific coordinates,
please contact the submitter of this circular by email.

W. Fong, B. Rothberg, J. Hill, P. Milne, N. Smith and D. Zaritsky
(University of Arizona) report on behalf of the AZTEC (Arizona Transient
Exploration and Characterization) team:

"We observed the field of the Fermi/LAT candidate (Omodei et al., GCN
21227
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 ) with the Large Binocular Camera (LBC) mounted on the 2x8.4-meter
Large Binocular Telescope (LBT) on Mount Graham, Arizona beginning on 2017
Jun 10.156 UT (2.07 days post-trigger; LSC/Virgo et al. GCN 21221
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 ). We
obtained 26x30-sec of i-band imaging in 1.7" seeing at a mean airmass of
2.2. The observations cover 88% of the Fermi/LAT localization region (90%
confidence; Omodei et al., GCN 21227
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 ), as well as the positions of
Swift/XRT Sources 1-4 (Evans et al.; GCN 21233
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 ).

Inspection of the LBT observations relative to Pan-STARRS1 archival imaging
reveals no new sources in or around the positions of XRT Sources 1-4.
Moreover, photometry of the known optical sources are consistent with the
archival PS1 and SDSS values within the 1-sigma uncertainties,
corroborating the conclusions from shallower imaging with NOWT (Xu et al.,
GCN 21236
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 ) and Swift/UVOT (Emery et al., GCN 21235
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 ). Calibrated to SDSS
stars in the field, we estimate a 3-sigma limiting magnitude of i_AB>22.4
mag for the observations.

We thank LBT Director Christian Veillet for awarding this observing time."

W. Fong, P. Milne, N. Smith and D. Zaritsky (University of Arizona) report
on behalf of the AZTEC (Arizona Transient Exploration and Characterization)
team:

"We observed the field of the Fermi/LAT candidate (Omodei et al., GCN
21227
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 ) with the Wide Field Camera (WFCAM) mounted on the 3.8-m United
Kingdom Infrared Telescope (UKIRT) on Mauna Kea beginning on 2017 Jun 9.238
UT (1.15 days post-trigger; LSC/Virgo et al. GCN 21221
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 ). We obtained a
total of 360-sec of J-band imaging in 1.4" seeing at a mean airmass of 1.8.
The observations cover the entire Fermi/LAT localization region (90%
confidence; Omodei et al., GCN 21227
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 ), as well as the positions of all
Swift/XRT sources reported in Evans et al. (GCN 21233
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 ).

To assess variability, we obtained a second set of observations beginning
on 2017 Jun 10.240 UT (2.16 days post-trigger and 24.0 hr after the initial
UKIRT observations). These observations cover only 75% of the Fermi/LAT
localization area, as well as the positions of XRT Sources 2-7.

We perform photometry of all known near-IR sources in or around the
positions of the XRT sources, and find no evidence for variability relative
to archival 2MASS values. Digital image subtraction of the two UKIRT epochs
using the ISIS software package reveals no residuals, indicating no
variability from 1.15 to 2.16 days post-trigger for 75% of the LAT
localization region, to a 3-sigma limit of J>18.9 AB mag. We note that this
preliminary analysis is based on reductions produced by the quick-look
pipeline ORAC-DR, and a final reduction of the images are expected to be at
least ~1.5 mag deeper.

We thank Sam Benigni and Watson Varricatt for their assistance in planning
and executing these observations."

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

HAWC performed a follow-up of LIGO trigger G288732. At the time of the trigger (2017-06-08 02:01:16 UTC) there was no overlap between HAWC field of view (FOV) and the LIGO Bayester probability contour, so it was not possible to perform a coincidence search in short time scales.

The LIGO contour entered HAWC FOV at around 2017-06-09 16:00 UTC and left it ~8hr later. The most probable location reached a zenith angle of ~10deg at culmination. We integrated this period for a total exposure of ~6hrs on each location of the ~70% of the LIGO probability contour observed. There were no significant detections.

Using this same integration period we followed-up the weak candidate reported by the Fermi-LAT team (R.A.,Dec.=128.11, 43.3, GCN circular 21227
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 ). The most significant location 2deg around the Fermi LAT trigger corresponds to 2.1 standard deviations pre-trials (R.A.,Dec.=128.4, 42.72). We set a 95% upper-limit in this location of 4.6e-11 (E/1TeV)^-2.5 TeV^-1 cm^-2 s^-1.

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.

Tomoki Morokuma (The University of Tokyo), Masaomi Tanaka (National 
Astronomical Observatory of Japan), Nozomu Tominaga (Konan University),
Shigeyuki Sako, Ryou Ohsawa, Mamoru Doi, Kentaro Motohara (The 
University of Tokyo) on behalf of J-GEM collaboration

We report optical imaging follow-up observations in an error region of 
the possible electromagnetic counterpart of G288732 (GCN 21221
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 ) 
discovered with Fermi LAT (Omodei et al. 2017, GCN, 21227). We observed 
the field with 1.05-m Kiso Schmidt telescope and its 2.2 deg x 2.2 deg 
field-of-view camera, Kiso Wide Field Camera (KWFC; Sako et al. 2012, 
SPIE, 8446, 84466L). We took two consecutive 1-sec exposures twice in 
i-band on June 9.483, 9.489, 9.527, and 9.529, 2017 UT, roughly 123 ks 
after the GW detection. The median depth of the images is 15.6 mag (AB, 
5 sigmas). Although there is a 1.5 arcmin gap in Declination because of 
the spatial gap of the CCDs, we covered almost the entire error field of 
the possible Fermi LAT detection. We compared the detected source 
catalogs with the public Pan-STARRS1 catalog (Chambers et al. 2016, 
arXiv:1612.05560
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 ) and do not find any new transient sources within the 
Fermi LAT error circle.  All the seven Swift XRT sources reported
in Evans et al. (2017, GCN 21233
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 ) were covered by our observations and
the source 7 is detected in our images with almost constant brightness
of i=12.8 mag.

[GCN OPS Note(14jun17): Per author's request, the phase
"were covered by our observations" was added to the last sentence.]

Alessandra Corsi (TTU) reports on behalf of a larger collaboration:

We observed the position (R.A.,Dec.=128.11, 43.39, J2000) of the Fermi/LAT candidate 
(Omodei et al. LVC GCN #21227
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 ) identified in the error region of LIGO/Virgo trigger 
G288732 (LVC GCN #21221
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 ) with the Karl G. Jansky Very Large Array (VLA) in its C 
configuration. The observations started on 2017 Jun 12 23:08:34 UTC, ended on 2017 
Jun 13 01:08:15 UTC, and were carried out in L-band (nominal central frequency of 
~1.4 GHz). The analysis of the collected data is in progress. Further observations 
are planned.

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


GCN 21227
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  (Omedi et al.) reported detection of a weak gamma-ray
candidate with Fermi/lAT at position R.A.,Dec.=128.11, 43.39, (J2000)
with a localization error of 0.24 degree, which is within the skymap
of the LIGO GW Binary Merger Candidate G288732 (GCN 21221
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 , Becsy et
al.), discovered at 2017-06-08 02:01:16.492 UTC (57912.08421866)

We report that we observed the Fermi/LAT postion with the Pan-STARRS1
telescope (Chambers et al. arXiv:1612.05560
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 ). We began taking data at
2017-06-09T 06:03:40 UT, centered on the Fermi position with a set of
8 dithered exposures in i and z band filters. The PS1 camera 
encloses a circle of 2.9 degree diamater, and therefore enclosed the 
whole of the Fermi/LAT error box. 

Difference images were produced by subtracting the Pan-STARRS1 3Pi
reference image from these separate exposures and a nightly combined
stack of the dithers (3Pi data described in Chambers et
al. arXiv:1612.05560
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 , and available at http://panstarrs.stsci.edu).
Using techniques discussed in Smartt et al. (2016, MNRAS, 462, 4094),
we located and vetted transients with quality filters and a machine
learning algorithm on the difference images.

No fast evolving transients (with variable lightcurves) were found
during the first night of data (MJD ~ 57913.25 to 57913.30) in the
individual 240s exposures, with limits of z > 18.5 +/- 0.5 (given the
airmass range of 1.9 - 2.8 and poor image quality).

Three transients were found in the stacked data covering several 
nights between 57913 and 57924. However all three are outside the
error radius of 0.24 degrees from Fermi/LAT. In summary, no possible
optical counterpart to the Fermi/LAT source is detected to 
i,z ~ 18.5 (within 24hrs) and i,z ~ 20.5 (daily stacked limits up to 
5 days after). 

The detected sources are below (where AngSep = angular separation
from the Fermi/LAT position in degrees)  

Name      RA (J2000)   Dec (J2000)  Disc. MJD  Disc Mag    AngSep 
PS17diu   08 35 24.13  +44 00 29.5  57913.26    18.82 (z)  0.82
PS17dit   08 27 39.44  +42 36 36.2  57916.28    20.56 (i)  0.78
PS17djl   08 30 31.25  +43 55 04.2  57916.29    20.45 (i)  0.63

PS17diu is associated with SDSS J083524.25+440029.3, an r=19.36 mag
galaxy with a host photoZ=0.083 (+/- 0.038) implying a transient M_i =
-19.36. The lightcurve is relatively flat over 10 days. This is likely
an old SN, and this is likely an old SN around peak.

PS17dit is likely associated with 2MASX J08273960+4236311; a 18.50 mag
galaxy with z=0.151, implying a transient at M = -18.8. The lightcurve
is flat for 4 days, and this is likely an old SN around peak.

PS17djl is likely associated with SDSS J083031.05+435504.3; an r=19.81
mag galaxy with A host photoZ=0.217 (+/- 0.051) implying a transient
at M = -19.7. Again, the lightcurve is flat for 4 days, also
suggesting this is likely an old SN around peak.

Adam Goldstein (USRA), Rachel Hamburg (UAH), and Colleen Wilson-Hodge
(NASA/MSFC) report on behalf of the GBM-LIGO Group:
Lindy Blackburn (CfA), Michael S. Briggs (UAH), Jacob Broida (Carleton
College), Eric Burns (UAH), Jordan Camp (NASA/GSFC), Tito Dal Canton
(NASA/GSFC), Nelson Christensen (Carleton College), Valerie Connaughton
(USRA), C. Michelle Hui (NASA/MSFC), Pete Jenke (UAH), Dan Kocevski
(NASA/MSFC), Nicolas Leroy (LAL), Tyson Littenberg (NASA/MSFC), Julie
McEnery (NASA/GSFC), Rob Preece (UAH), Judith Racusin (NASA/GSFC), Peter
Shawhan (UMD), Karelle Siellez (GA Tech), Leo Singer (NASA/GSFC), John
Veitch (Birmingham), Peter Veres (UAH)

Fermi GBM observed 89% of the Bayestar sky map at the time of the LIGO
trigger, and we set the following flux upper limits for the entire visible
sky map (excluded region is a circle with radius of 68 degrees centered on
RA, Dec = 197.9, 19.5).

Using a hard Band function with (Epeak, alpha, beta) = (500 keV, -0.5,
-2.5), we set a 3 sigma, 1-second-averaged flux upper limit for any
transient within 30 s of the LIGO trigger time in the 10-1000 keV band
ranging from 4.6e-7 to 9.2e-7 erg/s-cm^2.  Using an exponentially cut-off
power law parametrized with (Epeak, index) = (566 keV, -0.42), which
represents the average GBM-triggered short GRB, the upper limit ranges from
5.1e-7 to 9.8e-7 erg/s-cm^2.

Using the Earth Occultation technique [1] to estimate the amount of
persistent emission during a 48-hour period centered on the LIGO trigger
time, we place the following range of 3-sigma day-averaged flux upper
limits based on observed sources over the entire LIGO sky map:

Energy       min  max  median
--------------------------------
 12- 27 keV: 0.07 0.50 0.09 Crab
 27- 50 keV: 0.12 0.71 0.16 Crab
 50-100 keV: 0.18 0.97 0.23 Crab
100-300 keV: 0.33 1.88 0.41 Crab
300-500 keV: 2.25 14.9 2.84 Crab

These limits are based on the minimum requirement that each source in the
Earth Occultation catalog was Earth-occulted at least 6 times in each of
the 24 hour periods preceding and following the LIGO trigger and that the
occultations were well separated from nearby bright sources.

The location of the Fermi/LAT candidate (Omodei et al., LVC GCN #21227
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 ) was
behind the Earth at the time of the LIGO trigger. The location came out
from behind the Earth at ~85 s after the LIGO trigger and was visible until
Fermi entered the South Atlantic Anomaly (SAA) ~1 hour later and was then
behind the Earth again after Fermi exited the SAA. During this one hour
window, the targeted search ([2], [3]) found three long and spectrally soft
candidates (False Alarm Rates of 1 per 2.2 hours, 1 per 1.1 hours, and 1
per 0.7 hours), all of which localize to the Galactic plane and far from
the LAT candidate location.  At ~48 minutes into this one hour window
(518583038.924 MET / 2017-06-08 02:50:33.924 UTC) another, spectrally
harder, candidate was found with a duration of ~0.5 s with a False Alarm
Rate of ~1 per 1.5 hours. An initial localization of this candidate
indicates that the LAT candidate location is within the 2-sigma
statistical-only confidence region.  Follow-up analysis and classification
of this candidate is inconclusive at this time, as is any potential
association with the LAT candidate.  Absent of any GBM counterpart to the
LAT candidate, we set a 3-sigma, 1-second-averaged flux upper limit that
ranges from 4.7e-7 to 5.6e-7 erg/s-cm^2 during this time window.

[1] C. Wilson-Hodge et al. 2012, ApJS, 201, 33
[2] L. Blackburn et al. 2015, ApjS 217, 8
[3] A. Goldstein et al. arXiv:1612.02395
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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
event G288732 (2017-06-08 02:01:16.492 UTC, hereafter T0;
LIGO/VIRGO Collaboration GCN Circ. 21221
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 ).

No triggered KW event happened from ~3 hours before to ~2.6 days
after T0. The closest waiting-mode event was ~7.5 hour after T0.
Using waiting-mode data within the interval T0 +/- 100 s,
we found no significant (> 5 sigma) excess over the background
in both KW detectors on temporal scales from 2.944 s to 100 s.

We estimate an upper limit (90% conf.) on the 10 keV ��� 10 MeV fluence
to 8.3x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a
typical KW short GRB spectrum (an exponentially cut off power law with
alpha=-0.5 and Ep=500 keV). For a typical long GRB spectrum (the Band
function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding
limiting peak flux is 3.0x10^-7 erg/cm^2/s (10 keV - 10 MeV, 2.944 s scale).

All the quoted values are preliminary.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We have re-analysed offline noise-subtracted data for the LIGO Hanford
Observatory (H) and the LIGO Livingston Observatory (L) around the time of
the binary black hole merger event G288732 / GW170608 (GCNs 21221
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  and
21239
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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-P.fits.gz, is available
for retrieval from the GraceDB event page:

https://gracedb.ligo.org/events/G288732

The 50% and 90% credible regions span about 170 and 520 square degrees,
respectively.

This is the preferred sky map at this time, and the version that will
appear in LVC 2017 ("GW170608: Observation of a 19-solar-mass binary black
hole coalescence", in preparation).