LIGO/Virgo S190915ak

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, 
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov 
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile 
(Observatorio Astronomico Felix Aguilar OAFA),

H.Levato 
(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE),

R. Rebolo, M. Serra 
(The Instituto de Astrofisica de Canarias),

D. Buckley 
(South African Astronomical Observatory),

O.A. Gres, N.M. Budnev, O.Ershova 
(Irkutsk State University, API),

A. Tlatov, D. Dormidontov 
(Kislovodsk Solar Station of the Pulkovo Observatory),

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




MASTER-Kislovodsk robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the LIGO/Virgo S190915ak errorbox  20 sec after notice time and 488 sec after trigger time at 2019-09-16 00:05:10 UT, with upper limit up to  18.0 mag. The observations began at zenit distance = 66 deg. The sun  altitude  is -28.9 deg. 

MASTER-Tavrida robotic telescope  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the LIGO/Virgo S190915ak errorbox  42 sec after notice time and 510 sec after trigger time at 2019-09-16 00:05:32 UT, with upper limit up to  17.9 mag. The observations began at zenit distance = 66 deg. The sun  altitude  is -32.6 deg. 

MASTER-IAC robotic telescope  located in Spain (IAC Teide Observatory) started inspect of the LIGO/Virgo S190915ak errorbox  58 sec after notice time and 526 sec after trigger time at 2019-09-16 00:05:48 UT, with upper limit up to  15.4 mag. The observations began at zenit distance = 80 deg. The sun  altitude  is -56.6 deg. 

The galactic latitude b = -60 deg., longitude l = 98 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/ligo_1.php?id=10805

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

     538 | 2019-09-16 00:05:10 |   MASTER-Kislovodsk | (12h 28m 43.081s , +69d 10m 37.29s) |   C |   100 | 17.9 |        
     538 | 2019-09-16 00:05:10 |   MASTER-Kislovodsk | (12h 51m 21.032s , +68d 43m 30.04s) |   C |   100 | 18.0 |        
     561 | 2019-09-16 00:05:32 |      MASTER-Tavrida | (12h 37m 08.804s , +69d 06m 05.53s) |   C |   100 | 16.9 |        
     561 | 2019-09-16 00:05:32 |      MASTER-Tavrida | (12h 39m 58.560s , +69d 11m 14.24s) |   C |   100 | 17.9 |        
     582 | 2019-09-16 00:05:48 |          MASTER-IAC | (12h 38m 17.588s , +69d 16m 19.88s) |  P| |   110 | 14.9 |        
     582 | 2019-09-16 00:05:48 |          MASTER-IAC | (12h 40m 14.677s , +69d 12m 29.84s) |  P- |   110 | 15.4 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190915ak during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-09-15
23:57:02.691 UTC (GPS time: 1252627040.691). The candidate was found
by the GstLAL [1], SPIIR [2], CWB [3], and MBTAOnline [4] analysis
pipelines.

S190915ak is an event of interest because its false alarm rate, as
estimated by the online analysis, is 9.7e-10 Hz, or about one in 32
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S190915ak

The classification of the GW signal, in order of descending
probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), MassGap
(<1%), or NSBH (<1%).

Assuming the candidate is astrophysical in origin, there is strong
evidence against the lighter compact object having a mass < 3 solar
masses (HasNS: <1%). Using the masses and spins inferred from the
signal, there is strong evidence against matter outside the final
compact object (HasRemnant: <1%).

One sky map is available at this time and can be retrieved from the
GraceDB event page:
 * bayestar.fits.gz, an updated localization generated by BAYESTAR
[5], distributed via GCN notice about 6 minutes after the candidate trigger time.
For the bayestar.fits.gz sky map, the 90% credible region is 528 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1557 +/- 381 Mpc (a posteriori mean +/- standard
deviation).

For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.

 [1] Messick et al. PRD 95, 042001 (2017)
 [2] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [3] Klimenko et al. PRD 93, 042004 (2016)
 [4] Adams et al. CQG 33, 175012 (2016)
 [5] Singer & Price PRD 93, 024013 (2016)

[GCN OPS NOTE(15sep19): Per author's request, "trigger time." was added
to the end of the first sentence in the fifth paragraph.]

IceCube Collaboration (http://icecube.wisc.edu/) reports:

Searches [1,2] for track-like muon neutrino events detected by IceCube
consistent with the sky localization of gravitational-wave candidate
S190915ak
 in a time range of 1000 seconds [3] centered on the alert event time
(2019-09-15 23:48:42.691 UTC to 2019-09-16 00:05:22.691 UTC) have been
performed.  During this time
period IceCube was collecting good quality data.  No significant track-like
events are found in spatial coincidence of S190915ak calculated from the map
circulated in the 1-Preliminary notice.

IceCube's sensitivity assuming an E^-2 spectrum (E^2 dN/dE) to neutrino
point sources within the locations spanned by the 90% spatial  containment
of S190915ak ranges from  0.032 to 0.083 GeV cm^-2 in a 1000 second
time window.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector
operating at the geographic South Pole, Antarctica. The IceCube realtime
alert point of contact can be reached at roc@icecube.wisc.edu


[1] Bartos et al. arXiv:1810.11467
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  (2018) and Countryman et
al.arXiv:1901.05486
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  (2019)
[2] Braun et al., Astroparticle Physics 29, 299 (2008)
[3] Baret et al., Astroparticle Physics 35, 1 (2011)

Francesca Onori, Antonio Martin-Carrillo
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of S190915ak (GCN 25753
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 ).

At the time of the event (2019-09-15 23:57:02 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 94 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(8.3% of optimal) response of ISGRI, strongly suppressed (24% of
optimal) response of IBIS/Veto, and near-optimal (8 8% of optimal)
response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.1).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2e-07 erg/cm^2 (within the
50% probability containment region of the source localization) for a
burst lasting less than 1 s with a characteristic short GRB spectrum
(an exponentially cut off power law with alpha=-0.5 and Ep=600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and
Ep=300 keV), the derived peak flux upper limit is ~1.8e-07 (5.2e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

For the mean reported distance 1557.0 Mpc this corresponds to the
limit on the total is otropic equivalent energy in 1 s of 5.9e+49 erg
for the short GRB spectrum and for a long GRB spectrum isotropic
equivalent luminosity in 1 s (8 s) of 4.5e+49 erg/s (1.5e+49 erg/s)

We report for completeness and in order of FAP, all excesses
identified in the search region. We find: 8 likely background
excesses:

scale | T | S/N | luminosity ( x 1e+50 erg/s) | FAP
0.05 | 0.193 | 3.1 | 3.61 +/- 1.38 +/- 2.12 | 0.0612
2.4 | 42.8 | 3.7 | 5.52 +/- 1.96 +/- 3.24 | 0.0912
2.1 | 79.6 | 3.4 | 5.8 +/- 2.09 +/- 3.41 | 0.319
0.4 | -44.5 | 4 | 16.4 +/- 4.83 +/- 9.64 | 0.368
0.2 | -6.88 | 3.1 | 18.3 +/- 6.84 +/- 10.7 | 0.585
0.8 | 152 | 4 | 11.5 +/- 3.41 +/- 6.76 | 0.609
3.75 | 144 | 3 | 3.75 +/- 1.57 +/- 2.2 | 0.911
0.05 | -4.46 | 3.2 | 3.77 +/- 1.38 +/- 2.21 | 0.971

Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.



All results quoted are preliminary.

This circular is an official product of the INTEGRAL Multi-Messenger
team.

[1] Savchenko et al. 2017, A&A 603, A46 [2] Savchenko et al. 2012, A&A
541A, 122S

GCN pipeline version: a76508f

https://sandbox.zenodo.org/record/369583

-- 
Dr. Francesca Onori
Postdoctoral Researcher
IAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy
e-mail: francesca.onori@inaf.it
Tel: +39 06 45488128

F. Lucarelli, F. Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, and Univ.
Roma Tor Vergata), C. Casentini, M. Cardillo, G. Piano, A. Ursi (INAF/IAPS),
C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, N. Parmiggiani
(INAF/OAS-Bologna), M. Pilia (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 S190915ak at T0 = 2019-09-15 23:57:02 (UT),
a preliminary analysis of the AGILE minicalorimeter (MCAL) triggered data found
no event candidates within a time interval covering -/+ 15 sec from the LIGO/Virgo T0.

At the T0, the whole S190915ak 90 c.l. localization region was accessible
to the AGILE MCAL. Three-sigma upper limits (ULs) are obtained for a 1 s
integration time at different celestial positions within the accessible S190915ak
localization region, from a minimum of 1.6E-06 erg cm^-2 to a maximum of
7.0E-06 erg cm^-2 (assuming as spectral model a single power law with photon
index 1.5).

The AGILE-MCAL detector is a CsI detector with a 4 pi FoV, sensitive in the
energy range 0.4-100 MeV. Additional analysis of AGILE data is in progress.

F. Verrecchia, F. Lucarelli (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS,
and Univ.Roma Tor Vergata), C. Casentini, M. Cardillo, G. Piano, A. Ursi
(INAF/IAPS), C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti,
N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (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 S190915ak at T0 = 2019-09-15
23:57:02.691 UTC a preliminary analysis of the AGILE exposure at T0
shows that the Gamma-Ray Imaging Detector (GRID) exposure covered the 22%
of the 90% c.l. localization region (LR) (33% of 90% c.l. localization
region (LR) is occulted by Earth) at an off-axis angle of about 70
degrees.

We performed an analysis of the GRID data in the energy range 50 MeV -
10 GeV on T0, where good exposure of the S190915ak 90% c.l. LR was
available.

No candidate gamma-ray transient was detected.

The following preliminary GRID values of 3-sigma upper limit (UL) are
obtained:
from 4.0e-06 to 1.0e-05 erg cm^-2 s^-1, with exposure of about 22% of
the LR over the time interval ( T0 -2s ; T0 + 2s ) at an off-axis angle
of about 70 degrees;
from 1.6e-06 to 1.0e-05 erg cm^-2 s^-1, with exposure of about 37% of
the LR over the time interval ( T0s ; T0 + 10s ) at an off-axis angle
of about 70 degrees;
from 3.9e-08 to 4.0e-07 erg cm^-2 s^-1, with exposure of about 75% of
the LR over the time interval ( T0s+ 100s ; T0 + 200s ) at an off-axis
angle between 30 and 70 degrees;

A map in Galactic coordinates showing the AGILE FoV at T0 is available
at the site:
https://tools.ssdc.asi.it/ImgView/Agile/AGILE_FOV_LIGOS190915ak_190915011120

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

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (APC/Universite de Paris), M. Colomer (APC/Universite de Paris), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite de Paris), 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 S190915ak event using the 90% contour of the Initial bayestar probability
map provided by the GW interferometers (GCN#25753
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 ). The ANTARES visibility at the time of the
alert, together with the 50% and 90% contours of the probability map are shown at http://antares.in2p3.fr/GW/S190915ak_Initial.png <http://antares.in2p3.fr/GW/S190915ak_Initial.png>.
Considering the location probability provided by the LIGO/Virgo collaborations, there is a
45.6% chance that the GW emitter was in the ANTARES **upgoing** field of view at the time of
the alert.

No up-going muon neutrino candidate events were recorded in the ANTARES sky during a
+/-500s time-window centered on the time 2019-09-15 23:57:02 and in the 90% contour of the S190915ak
event. The expected number of atmospheric background events in the region visible by ANTARES is
2.31e-04 in the +/- 500s time window. An extended search during +/- 1 hour gives no
up-going muon neutrino coincidence. The expected number of atmospheric background events in the
region visible by ANTARES is 1.66e-03 in this larger time window.

ANTARES is the largest undersea neutrino detector, installed in the Mediterranean Sea, and it is
primarily sensitive to neutrinos in the TeV-PeV  energy range. At 10 TeV, the median angular
resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a
competitive sensitivity to this position in the sky.

M. Serino, S. Sugita (AGU),
H. Negoro (Nihon U.),
N. Kawai (Tokyo Tech), 
M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.),
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, H. Nishida, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
M. Shidatsu (Ehime U.), M. Sugizaki, M. Oeda, K. Shiraishi (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, N. Isobe, R. Shimomukai, M. Tominaga (JAXA),
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.),
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.),
M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.),
T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
report on behalf of the MAXI team:

We examined MAXI/GSC all-sky X-ray images (2-20 keV)
after the LVC trigger S190915ak at 2019-09-15 23:57:02.690 UTC (GCN 25753
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 ).

At the trigger time of S190915ak, the high-voltage of MAXI/GSC was on,
but the FOV was out of the 90% credible region of the bayestar skymap.
The first one-orbit (92 min) scan observation with GSC after the event covered 35%
of the 90% credible region of the bayestar skymap from 00:26:35 to 00:50:01 UTC (T0+1773 to T0+3179 sec).

No significant new source was found in the region in the one-orbit scan observation.
A typical 1-sigma averaged upper limit obtained in one scan observation
is 20 mCrab at 2-20 keV.

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

M. Axelsson (KTH and Stockholm Univ.), S. Cutini (INFN Perugia), M. Arimoto (Kanazawa Univ.), N. Omodei (Stanford Univ.),  D. Kocevski (NASA/MSFC), F. Piron (CNRS/IN2P3/LUPM), F. Longo (Univ. and INFN Trieste) and E. Bissaldi (Politecnico and INFN Bari) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on Sep 15, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190915ak (GCN 25753
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 ).

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. Fermi-LAT had null instantaneous coverage of the LIGO probability region at the time of the trigger (T0 = 2019-09-15 23:57:02.691 UTC). Coverage of the region started around T0 + 2.5 ks, and reached 100% cumulative coverage at approximately T0 + 3.2 ks. 

We performed a search for a transient counterpart within the observed region of the 90% contour of the LIGO map in a fixed time window from T0 to T0 + 10 ks. No significant sources were found.

We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky, and no additional excesses were found.

Energy flux upper bounds for the fixed time interval between 100 MeV and 1 GeV for this search vary between 1.1E-10 and 5.3E-10 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Sara Cutini (sara.cutini@pg.infn.it). 

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.

E. Burns (NASA/GSFC) and C.A. Wilson-Hodge (NASA/MSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190915ak and using the initial bayestar skymap, Fermi-GBM was observing 98.0% of the localization probability at event time.

There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo detection of GW trigger S190915ak (GCN 25753
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 ). An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.

Part of the LVC localization region is behind the Earth for Fermi, located at RA=129.5, Dec=-19.0 with a radius of 67.5 degrees. We therefore set upper limits on impulsive gamma-ray emission for the LVC localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395
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 , we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):

Timescale  soft     norm     hard
--------------------------------------
0.128 s:   11      13      23
1.024 s:   2.5     3.2      6.9
8.192 s:   1.1     1.3     1.6

Assuming the median luminosity distance of 1557 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^50 erg/s):
Timescale  Soft     Normal   Hard
------------------------------------
0.128 s:    4.7      5.0      15
1.024 s:    1.1      1.2      4.4
8.192 s:    0.47     0.50     1.0

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (NASA/GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
A. P. Beardmore (U. Leicester), M. G. Bernardini (INAF-OAB),
A. A. Breeveld (MSSL-UCL), 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 (ASI-SSDC), S. Emery (UCL-MSSL),
P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU),
D. Hartmann (Clemson U.), J. A. Kennea (PSU),
N. Klingler (PSU), H. A. Krimm (NSF),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), 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. J. Page (UCL-MSSL), M. Perri (ASDC),
J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (Toronto),
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
LVC event S190915ak (LIGO/VIRGO Collaboration GCN Circ. 25753
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 ),
where T0 is the LVC trigger time (2019-09-15T23:57:02.690 UTC).

The center of the BAT field of view (FOV) at T0 is
RA = 144.711 deg,
DEC = 51.949 deg,
and the roll angle is 135.601 deg.
The BAT FOV (>10% partial coding) covers 85.57% of the integrated
LVC localization probability, and 84.76% of the galaxy convolved
probability (Evans et al. 2016). Note that the sensitivity in the BAT FOV
changes with the partial coding fraction. Please see the BAT FOV figure
in the summary page (link below) for the specific location of the LVC
region relative to the BAT FOV.

Within T0 +/- 100 s, 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. 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 ~ 1.05 x 10^-7 erg/s/cm^2.
Assuming a luminosity of ~ 2 x 10^47 erg/s (similar to GW170817)
and an average Epeak of ~ 400 keV for short GRBs (Bhat et al. 2016),
this flux upper limit corresponds to a distance of ~ 70.25 Mpc.

Event data is available from T0-101.315 to T0+98.701. No significant
detections are found in the 15-350 keV images created using intervals of
T0 to T0+0.1 s, T0-2 s to T0+8 s, and the whole event data range.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 13.67% of the integrated LVC
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 higher than those
within the FOV.

The results of the BAT analysis are available at
https://swift.gsfc.nasa.gov/results/BATbursts/team_web/S190915ak/web/source_public.html

P. S. Marrocchesi (U of Siena), A. Yoshida, T. Sakamoto, V. Pal'shin,
S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), 
S. Nakahira (RIKEN), Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), 
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger 
time of S190915ak T0 = 2019-09-15 23:57:02.691 UT (The LIGO Scientific
Collaboration and Virgo Collaboration, GCN Circ. 25753
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 ).

No CGBM on-board trigger occurred around the event time.  Based on the
LIGO-Virgo high probability localization region, the summed LIGO 
probabilities inside the CGBM HXM (7 - 3000 keV) and SGM 
(40 keV - 28 MeV) fields of view are 1 % and 2 %, respectively (and 100 % 
credible region of the initial localization map was above the horizon).
The HXM and SGM fields of view were centered at RA = 107.0 deg, 
Dec = -4.2 deg and RA = 99.7 deg, Dec = -11.1 deg at T0, respectively.

Based on the analysis of the light curve data with 0.125 sec time 
resolution from T0-60 sec to T0+60 sec, we found no significant excess
(signal-to-noise ratio >= 7) around the trigger time in either the HXM or
the SGM data.

The CALET Calorimeter (CAL) was operating in the high energy trigger
mode at the trigger time of S190915ak. Using the CAL data, we have
searched for gamma-ray events in the 10-100 GeV band from -60 sec
to +60 sec from the GW trigger time and found no candidates. There is
no significant overlap with the LIGO-Virgo high probability localization 
region. The CAL FOV was centered at RA=99.7 deg, Dec=-11.1 deg at T0.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We have conducted further analysis of the data from LIGO Hanford
Observatory (H1), LIGO Livingston Observatory (L1) and Virgo
Observatory (V1) around the time of the compact binary merger (CBC)
candidate S190915ak (GCN Circular 25753
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 ). Parameter estimation has
been performed using LALInference [1] and a new sky map,
LALInference.fits.gz, distributed via GCN Notice, is available for retrieval
from the GraceDB event page:

https://gracedb.ligo.org/superevents/S190915ak

The preferred sky map at this time is LALInference.fits.gz. The 90%
credible region is 318 deg2. Marginalized over the whole sky, the a
posteriori luminosity distance estimate is 1584 +/- 381 Mpc (a posteriori
mean +/- standard deviation).

For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.

 [1] Veitch et al. PRD 91, 042003 (2015)

D. A. Kann (HETH/IAA-CSIC), A. Simon (ASPD TSNUK), Z. Vidadi (Shao), S. 
Antier (APC), M. Boer (Artemis), N. Christensen (Artemis), L. Eymar 
(Artemis), A. Klotz (IRAP), S. Alishov (SHAO), K. Barynova (Kyiv Univ),  
D. Coward (OzGrav-UWA), K. Noysena (Artemis, IRAP),  S. Basa (LAM), D. 
Corre (LAL), M. Coughlin (Caltech), J.G. Ducoin (LAL), B. Gendre 
(OzGrav-UWA), P. Hello (LAL), C. Lachaud (APC), N. Leroy (LAL), D. 
Turpin (NAOC) and X. Wang (THU)

report on behalf of the TAROT network and GRANDMA collaborations:

We performed tiled observations of LIGO/Virgo S190915ak event (GCN 
#25753
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 ) with the TAROT-Calern (TCA) telescope operating in the visible 
located at Calern site at the Cote d'Azur observatory. The observation 
started on 09/16/19 00:12:27 UTC which corresponds approximately to 16 
minutes after the GW trigger time.

We performed the following tiled observations :

+------------+------------+---------+---------+---------+
| TStart     | TEnd       | RA      | DEC     |   Proba |
| [UTC]      | [UTC]      | [deg]   | [deg]   |     [%] |
|------------+------------+---------+---------+---------|
| 2019-09-16 | 2019-09-16 | 195.545 | 68.682  |     1.0 |
| 00:12:27   | 23:06:42   |         |         |         |
| 2019-09-16 | 2019-09-16 | 187.785 | 66.826  |     0.7 |
| 00:19:13   | 23:13:29   |         |         |         |
| 2019-09-16 | 2019-09-18 | 190.68  | 68.682  |     1.1 |
| 00:54:58   | 01:52:26   |         |         |         |
| 2019-09-16 | 2019-09-17 | 185.815 | 68.682  |     0.5 |
| 01:20:35   | 01:17:26   |         |         |         |
| 2019-09-16 | 2019-09-18 | 192.342 | 66.826  |     1.6 |
| 01:27:23   | 03:10:13   |         |         |         |
| 2019-09-16 | 2019-09-16 | 186.244 | 70.538  |     0.4 |
| 01:34:07   | 22:57:41   |         |         |         |
| 2019-09-16 | 2019-09-17 | 191.538 | 70.538  |     0.8 |
| 02:51:43   | 01:10:45   |         |         |         |
| 2019-09-16 | 2019-09-17 | 168.392 | 77.96   |     0.2 |
| 23:58:22   | 00:04:42   |         |         |         |
| 2019-09-17 | 2019-09-18 | 195.774 | 64.971  |     1.9 |
| 00:05:13   | 02:57:21   |         |         |         |
| 2019-09-17 | 2019-09-17 | 161.664 | 74.249  |     0.1 |
| 00:17:49   | 02:54:26   |         |         |         |
| 2019-09-17 | 2019-09-17 | 196.899 | 66.826  |     1.3 |
| 00:24:37   | 21:01:18   |         |         |         |
| 2019-09-17 | 2019-09-17 | 191.538 | 64.971  |     1.5 |
| 02:15:22   | 20:54:35   |         |         |         |
| 2019-09-17 | 2019-09-17 | 180.95  | 68.682  |     0.4 |
| 02:41:18   | 02:47:37   |         |         |         |
| 2019-09-17 | 2019-09-17 | 196.541 | 50.125  |     5.3 |
| 19:19:28   | 21:40:15   |         |         |         |
| 2019-09-17 | 2019-09-17 | 195.704 | 51.981  |     4.9 |
| 19:30:30   | 19:34:40   |         |         |         |
| 2019-09-17 | 2019-09-17 | 193.706 | 50.125  |     2.1 |
| 20:16:20   | 20:22:40   |         |         |         |
| 2019-09-17 | 2019-09-17 | 196.832 | 46.414  |     1.7 |
| 20:28:50   | 20:35:09   |         |         |         |
| 2019-09-17 | 2019-09-17 | 194.796 | 63.115  |     1.5 |
| 20:41:28   | 20:47:47   |         |         |         |
| 2019-09-17 | 2019-09-17 | 197.021 | 55.692  |     1.3 |
| 21:01:43   | 21:08:03   |         |         |         |
| 2019-09-17 | 2019-09-17 | 192.753 | 51.981  |     1.1 |
| 21:13:51   | 21:20:10   |         |         |         |
| 2019-09-17 | 2019-09-17 | 200.95  | 53.837  |     1.1 |
| 21:20:24   | 21:26:44   |         |         |         |
| 2019-09-17 | 2019-09-17 | 198.655 | 51.981  |     4.2 |
| 21:46:35   | 21:52:54   |         |         |         |
| 2019-09-17 | 2019-09-17 | 197.873 | 53.837  |     3.3 |
| 21:53:19   | 21:59:38   |         |         |         |
+------------+------------+---------+---------+---------+

TStart and TEnd refers respectively to the time of the first and last 
exposure for a given tile. Observations are not necessarily continuous 
in this interval.

The Probability refers to the 2D spatial probability of the GW skymap 
enclosed in a given tile. Each tile is 1.9x1.9 degrees. These 
observations cover about 36% the cumulative probability of the 
LALInference skymap available on Sep 17, 2019 14:16:39 UTC.

The typical limiting magnitude is 18.0 for a 60.0 s exposure.

The coverage map is available at: 
https://grandma-owncloud.lal.in2p3.fr/index.php/s/55vKDfmLJzbHyBn

No significant transient candidates were found during our low latency 
analysis.

GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger 
Addicts) is a network of robotic telescopes connected all over the world 
with both photometry and spectroscopy capabilities for Time-domain 
Astronomy (https://grandma.lal.in2p3.fr/). Details on the TCA telescope  
are available on the GRANDMA web pages or on  http://tarot.obs-hp.fr/.