LIGO/Virgo S190521g

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

IceCube has performed a search for track-like muon neutrino events
consistent with the sky localization of S190521g-1-Preliminary in a time
range of 1000
seconds centered on the alert event time (2019-05-21 02:54:09.447 UTC to
2019-05-21 03:10:49.447 UTC)
during which IceCube was collecting good quality data.
No track-like events are found in spatial coincidence with the 90% spatial
containment of S190521g-1-Preliminary calculated from the map
circulated in the preliminary notice.

IceCube's sensitivity to point sources within the location spanned by the
90% spatial containment of S190521g-1-Preliminary ranges from
0.039 to 0.966 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

V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa,
A.Kuznetsov, V.V.Chazov, D. Vlasenko
(Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University)

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

K. Ivanov, O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev, V. Poleshchuk
(Irkutsk State University)

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

R. Podesta, Carlos Lopez and F. Podesta
(Observatorio Astronomico Felix Aguilar (OAFA))

Hugo Levato and Carlos Saffe
(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE))

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
(The Instituto de Astrofisica de Canarias)

D. Buckley, S. Potter, A. Kniazev, M. Kotze
(South African Astronomical Observatory)



MASTER-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the LIGO/Virgo S190521g errorbox  429 sec after trigger time at 2019-05-21 03:09:38 UT, with upper limit up to  19.4 mag. The observations began at zenit distance = 60 deg. The sun  altitude  is -28.2 deg. 

MASTER-OAFA robotic telescope  located in Argentina (OAFA observatory of San Juan National University) started inspect of the LIGO/Virgo S190521g errorbox  578 sec after trigger time at 2019-05-21 03:12:07 UT, with upper limit up to  16.4 mag. The observations began at zenit distance = 133 deg. The sun  altitude  is -69.1 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=10405

We obtain a following upper limits.  

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

     474 | 2019-05-21 03:09:38 |         MASTER-SAAO | (  0h 29m 35.15s , -66d 12m 40.55s) |   C |    90 | 18.4 |        
     599 | 2019-05-21 03:09:38 |         MASTER-SAAO | (  0h 29m 35.15s , -66d 12m 40.54s) |   C |   340 | 19.4 |  Coadd 
     604 | 2019-05-21 03:11:37 |         MASTER-SAAO | (  0h 29m 56.68s , -66d 12m 35.01s) |   C |   110 | 18.6 |        
     639 | 2019-05-21 03:12:07 |         MASTER-OAFA | (  0h 18m 54.28s , -66d 16m 16.13s) |   C |   120 | 16.3 |        
     757 | 2019-05-21 03:13:55 |         MASTER-SAAO | (  0h 29m 57.51s , -66d 12m 34.78s) |   C |   140 | 18.6 |        
    1057 | 2019-05-21 03:18:35 |         MASTER-OAFA | (  0h 18m 54.17s , -66d 16m 16.79s) |   C |   180 | 16.4 |        
Filter C is a clear (unfiltred) band. 


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

Maeve Doyle (UCD, Ireland), Enrico Bozzo,
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 <https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration>

Using INTEGRAL/SPI-ACS realtime data (following Savchenko et al. 2017,
A&A 603, A46) we have performed a search for a prompt gamma-ray
counterpart of S190521g.

At the time of the event (2019-05-21 03:02:29 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 23 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(16% of optimal) response of ISGRI, strongly suppressed (25% of
optimal) response of IBIS/Veto, and somewhat suppressed (56% of
optimal) response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in Savchenko et al. 2012, A&A 541A, 122S) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2.3e-07 erg/cm^2 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 ~2e-07 (8.6e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190521g during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-05-21
03:02:29.447 UTC (GPS time: 1242442967.447). The candidate was found
by the PyCBC Live [1], CWB [2], GstLAL [3], and SPIIR [4] analysis
pipelines.

S190521g is an event of interest because its false alarm rate, as
estimated by the online analysis, is 3.8e-09 Hz, or about one in 8
years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190521g

The classification of the GW signal, in order of descending
probability, is BBH (97%), Terrestrial (3%), BNS (<1%), NSBH (<1%),
or MassGap (<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

For the bayestar.fits.gz sky map, the 90% credible region is 1163 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 663 +/- 156 Mpc (a posteriori mean +/- standard
deviation).

We have reason to believe that the distance may be underestimated
because different search pipelines have reported a range of distances.
The two-dimensional sky map (right ascension and declination)
is in good agreement across pipelines. Offline analyses to resolve
this issue are ongoing.

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] Nitz et al. PRD 98, 024050 (2018)
 [2] Klimenko et al. PRD 93, 042004 (2016)
 [3] Messick et al. PRD 95, 042001 (2017)
 [4] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [5] Singer & Price PRD 93, 024013 (2016)

The HAWC Collaboration (https://www.hawc-observatory.org) reports:

The HAWC Collaboration performed a follow-up of the gravitational wave
trigger S190521g. At the time of the trigger the HAWC
local zenith was oriented towards (RA, Dec) = (186.5 deg, 19.1 deg).
30% of the GW candidate sky location probability fell within our
observable field of view (0-45 deg zenith angle).

We performed a search for a short timescale emission using 6 sliding
time windows (dt = 0.3s, 1s, 3s, 10s, 30s and  100s), shifted forward
in time by 20% of their width. We searched the 95% probability
containment area in a timescale-dependent time period, from t0-5dt to
t0+10dt, where t0 is the time of the GW trigger.

No significant gamma-ray detection above the background was observed.

The sensitivity of this analysis is greatly dependent on zenith angle,
ranging from 0.0 deg to 45.0 deg for the area searched in this
analysis. The 5sigma detection sensitivity to a 1s (100s) burst in the
80-800GeV energy range goes from 1.2e-06 erg/cm^2 to 1.1e-04 erg/cm^2
(6.4e-06 erg/cm^2 to 5.0e-04 erg/cm^2), depending on the zenith
angle.

HAWC is a TeV gamma ray water Cherenkov array located in the state of
Puebla, Mexico. It is sensitive to the energy range ~0.1-100TeV, and
monitors 2/3 of the sky every day with an instantaneous field-of-view
of ~2 sr.

C.Casentini (INAF/IAPS), F.Verrecchia (SSDC, and INAF/OAR), M. Tavani
(INAF/IAPS, and Univ. Roma Tor Vergata), M.Cardillo, G.Piano, A.Ursi
(INAF/IAPS), F.Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli,
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 S190521g at T0 = 2019-05-21 03:02:29
(UT), a preliminary analysis of the AGILE minicalorimeter (MCAL) triggered
data found no event candidates within a time interval covering 100 sec
preceding the LIGO-Virgo T0. Later times were not covered by MCAL exposure
because of SAA interruption, until about + 800 sec from T0.

Three-sigma upper limits (ULs) are obtained for a 1 s integration time at
different celestial positions within the accessible S190521g 90% c.l.
localization region (almost 60% of the given GW contour), from a minimum of
2.08E-06 erg cm^-2 to a maximum of 8.31E-06 erg cm^-2 (assuming as spectral
model a single power law with photon index 1.5). The average off-axis angle
is about 60 degrees.

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.

Maeve Doyle (UCD, Ireland), Enrico Bozzo,
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 combination of INTEGRAL all-sky detectors (following Savchenko
et al. 2017, A&A 603, A46): SPI/ACS, IBIS/Veto, and IBIS we have
performed a search for a prompt gamma-ray counterpart of S190521g (GCN
24621
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 ).

At the time of the event (2019-05-21 03:02:29 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 23 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(16% of optimal) response of ISGRI, strongly suppressed (25% of
optimal) response of IBIS/Veto, and somewhat suppressed (56% of
optimal) response of SPI-ACS.

This orientation was relatively favorable for an IBIS/PICsIT observation, which 
is why we have performed a search for any impulsive signal near the 
time of the event in INTEGRAL IBIS/PICsIT data. We do not find any significant signal 
in this data. Furthermore, a fraction of the LIGO/Virgo GW localization probability 
occurred within the FoV of the coded mask imager IBIS/ISGRI, which is inspected by the 
INTEGRAL Burst Alert System (IBAS). No IBAS trigger occurred around the time of the event.

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 Savchenko et al. 2012, A&A 541A, 122S) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 1.7e-07 erg/cm^2 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 ~1.4e-07 (5.2e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (APC/Universite Paris Diderot), M. Colomer (APC/Universite Paris Diderot)), 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 S190521g event using the 90% contour of the bayestar probability map provided by the GW interferometers (GCN#24621
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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 https://www.cppm.in2p3.fr/~dornic/events_runo3/S190521g.png. Considering the location probability provided by the LIGO/Virgo collaborations, there is a 56% 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 (2019-05-21
03:02:29.447 UT) and in the 90% contour of the S190521g event. The expected number of atmospheric background events in the region visible by ANTARES is 2.4e-4 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 1.7e-3 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. Axelsson (KTH and Stockholm Univ.), D. Tak (Univ. of Maryland) and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on May 21, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190521g (GCN 24621
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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 a time, and "cumulative coverage" as the integral of the instantaneous coverage over time. Fermi-LAT had instantaneous coverage of ~15% of the LIGO probability at the time of the trigger (T0 = 2019-05-21 03:02:29.447 UTC), and reached 100% cumulative coverage after ~5.5 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 1.5e-10 and 2.2e-09 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Donggeun Tak (takdg123@umd.edu<mailto:takdg123@umd.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.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We have conducted further analysis of the LIGO and Virgo data around the
time of the compact binary coalescence (CBC) candidate S190521g
(GCN 24621
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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/S190521g

LALInference.fits.gz is the preferred sky map at this time.
The 90% credible region is 765 deg2. Marginalized over the whole sky,
the a posteriori luminosity distance estimate is 3931 +/- 953 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)

S. Poolakkil (UAH) and A. Goldstein (USRA) report on behalf of the
Fermi-GBM Team and the GBM-LIGO/Virgo group:

For S190521g, and using the updated LALInference skymap, Fermi-GBM was
observing 70.9% 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 S190521g (GCN 24621
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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 = 172.7 and Dec = -25.4 with a radius of 67.5 degrees.
We therefore set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like spectral 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 the remaining visible GW localization probability
(in units of erg/s/cm^2):

Timescale  soft     norm     hard
--------------------------------------
0.128 s:   7.6e-07  9.7e-07  1.8e-06
1.024 s:   2.6e-07  3.4e-07  5.2e-07
8.192 s:   6.7e-08  1.1e-07  1.9e-07

Assuming the median luminosity distance of ~3931 Mpc from the GW detection,
we estimate intrinsic luminosity upper limits of (1.9-22.5)E50 erg/s for the
soft template, (2.7-24.5)E50 erg/s for the normal template, and
(8.1-77.3)E50 erg/s for the hard template over the 1 keV-10 MeV energy
range.

Alan M. Watson (UNAM), Simone Dichiara (UMD), Nat Butler (ASU), Rosa L. Becerra (UNAM), Diego Gonz��lez (UNAM), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Margarita Pereyra (UNAM), Eleonora Troja (GSFC/UMD), and Tanner Wolfram (ASU) report:

We observed LIGO/Virgo S190519g (Mo et al, GCN Circ. 24621
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 ) with the DDOTI/OAN wide-field imager at the Observatorio Astron��mico Nacional on Sierra San Pedro M��rtir (http://ddoti.astroscu.unam.mx) on the night of 2019-04-21 UTC. 

We observed four fields covering a region of approximately 14 degrees in RA and 21 degrees in declination (280 square degrees) centered on 12:36:00 +28:20:00. This region includes about 20% of the probability in the initial localization map. We observed from 2019-05-21 04:27 UTC to 09:33 UTC (1.5 to 6.6 hours after the event). We obtained about 36 minutes total exposure on each field in the w filter.

We calibrate our images against the APASS catalog. Our 10-sigma limiting magnitude are typically w = 18.7 AB.

Comparing our 10-sigma detections against the USNO-B1 catalog, we detect no uncataloged sources with significant fading.

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

S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC),
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),
D. Hartmann (Clemson U.), J. A. Kennea (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. Perri (ASDC),
J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU),
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 S190521g (LIGO/VIRGO Collaboration GCN Circ. 24621
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 ),
where T0 is the LVC trigger time (2019-05-21T03:02:29.447 UTC).

The center of the BAT FOV at T0 is
RA = 169.185 deg,
DEC = 44.211 deg,
and the ROLL angle is 302.639 deg.
The BAT Field of View (>10% partial coding) covers 47.64% of the integrated
LVC localization probability, and 46.16% of the galaxy convolved
probability (Evans et al. 2016).

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 ~ 7.04 x 10^-8 erg/s/cm^2.

Event data are available from T0-91.427 to T0-88.355. No significant
detections are found in the 15-350 keV image made using the whole event
data duration.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 41.08% 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/S190521g/web/source.html

Y. Asaoka (Waseda U),  A. Yoshida, T. Sakamoto,
V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU),
K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
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),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

At the trigger time of the compact binary merger candidate S190521g,
T0 = 2019-05-21 03:02:29.447 UT (The LIGO Scientific Collaboration 
and  Virgo Collaboration, GCN Circ. 24621
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 ), the CALET Gamma-ray
Burst Monitor (CGBM) high voltages were off (from T0-8 min to 
T0+8 min).

The CALET Calorimeter (CAL) was operating in the high energy trigger 
mode at the trigger time of S190521g. Using 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.   The
90% upper limit of CAL is 6.0x10^-6 erg/cm2/s (10-100 GeV) when the
summed LIGO-Virgo probability reaches 30%. The CAL FOV was 
centered at RA=205.7 deg, Dec=49.2 deg at T0.

C. Cai, S. Xiao, Q. B. Yi, Q. Luo, C. K. Li, 
X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, 
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, 
Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team: 

Insight-HXMT was taking data normally around the reported LIGO/Virgo 
S190521g event (GCN #24621
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 ), trigger time 2019-05-21T03:02:29 UTC. 
At T0, more than 34% of the LIGO localization region was covered by 
Insight-HXMT without occultation by the Earth.

Within T0 +/- 100 s, no significant excess events (SNR > 3 sigma) are 
found in a search of the Insight-HXMT/HE raw light curves.

Assuming the GW counterpart GRB with three typical GRB Band spectral 
models, two typical duration timescales (1 s, 10 s) from the center 
of the LIGO-Virgo location probability map (RA=340 deg, DEC=-50 deg), 
the 5-sigma upper-limits fluence (0.2 - 5 MeV, incident energy) are 
reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):
1 s:   1.2e-07 erg cm^-2
10 s:  5.7e-07 erg cm^-2

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1 s:   1.7e-07 erg cm^-2
10 s:  7.2e-07 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1 s:   3.2e-07 erg cm^-2
10 s:  1.4e-06 erg cm^-2

All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (deposited energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the spacecraft.

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information could be found at: http://www.hxmt.org.

LIGO/Virgo S190521g: No optical counterpart from SVOM/GWAC observations.

D. Turpin (NAOC), N. Dagoneau (CEA/AIM), L.P. Xin (NAOC),
X.H. Han (NAOC), J.Y. Wei (NAOC), C. Wu (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. 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), P.P. Zhang (NAOC),
R.S. Zhang (NAOC), E.W. Liang (GXU), X.G. Wang (GXU), Z.G. Dai (NJU),
X.Y. Wang (NJU), Y.G. Yang (HBNU), J.R. Mao (YNAO), B. Cordier (CEA/AIM),
S. Basa (CNRS/LAM), J.L. Atteia (UPS/IRAP), D. G�tz (CEA/AIM),
A. Claret (CEA/AIM), N. Leroy (CNRS/LAL), C. Lachaud (CNRS/APC),
E. Le Floc'h (CEA/AIM), S.N. Zhang (IHEP), B.B. Wu (IHEP),
report on behalf of the SVOM Ground Follow-up Group:


We observed 12 sky regions (total: 241.9 square degrees) to cover the
initial skymap of the LIGO/Virgo trigger S190521g (GCN24621
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 ), with 
SVOM/GWAC, at Xinglong Observatory, equipped with a set of two types
of wide angle cameras: FFOV cameras (FOV~900 square degrees/camera,
aperture = 3.5cm) and JFOV cameras (FOV~150 square degrees/camera,
aperture = 18cm).
SVOM/GWAC currently comprises 4 FFOV cameras and 16 JFOV cameras,
working with unfiltered band. The observations are operated in time-series
mode, taking one exposure every 15 seconds (10s exposure + 5s readout).
We estimate a 31.6% prior probability that these 12 regions contain the
true location of the source.
The coordinates of the 12 regions and observation time are listed below:

# Ra[deg] Dec[deg] start-obs(UTC) end-obs(UTC) FoV
1 186.062 19.4675 2019-05-21 12:28:04 2019-05-21 13:58:31 12.5x12.5 deg
2 173.651 31.7854 2019-05-21 12:28:04 2019-05-21 13:58:10 12.5x12.5 deg
3 187.313 30.9042 2019-05-21 12:28:55 2019-05-21 13:58:10 12.5x12.5 deg
4 200.866 18.4278 2019-05-21 13:58:51 2019-05-21 16:14:36 12.5x12.5 deg
5 213.618 47.4480 2019-05-21 13:59:55 2019-05-21 16:15:18 12.5x12.5 deg
6 212.232 35.2260 2019-05-21 13:59:55 2019-05-21 16:15:18 12.5x12.5 deg
7 196.883 35.0781 2019-05-21 13:59:55 2019-05-21 16:15:07 12.5x12.5 deg
8 195.536 47.1398 2019-05-21 13:59:55 2019-05-21 16:15:07 12.5x12.5 deg
9 239.028 47.0970 2019-05-21 16:16:18 2019-05-21 17:10:37 12.5x12.5 deg
10 240.266 35.0818 2019-05-21 16:16:18 2019-05-21 17:10:37 12.5x12.5 deg
11 255.613 35.2164 2019-05-21 16:16:18 2019-05-21 17:10:33 12.5x12.5 deg
12 257.022 47.4364 2019-05-21 16:26:48 2019-05-21 17:10:33 12.5x12.5 deg
4 200.45 18.3189 2019-05-22 15:35:57 2019-05-22 15:45:16 12.5x12.5 deg
4 202.637 18.2594 2019-05-22 14:36:21 2019-05-22 14:57:49 12.5x12.5 deg
8 195.53 47.1473 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
7 196.874 35.0868 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
6 212.24 35.2348 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
5 213.618 47.4531 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
7 197.187 35.7065 2019-05-22 15:46:41 2019-05-22 15:58:26 12.5x12.5 deg
8 195.659 46.8473 2019-05-22 15:56:00 2019-05-22 15:58:26 12.5x12.5 deg
6 214.626 37.1103 2019-05-22 17:20:03 2019-05-22 17:58:29 12.5x12.5 deg
7 200.666 37.3979 2019-05-22 17:32:10 2019-05-22 17:58:27 12.5x12.5 deg
12 260.506 48.6905 2019-05-22 19:16:41 2019-05-22 19:19:30 12.5x12.5 deg
10 244.148 37.3798 2019-05-22 19:18:42 2019-05-22 19:19:30 12.5x12.5 deg
9 238.995 47.1164 2019-05-22 14:04:56 2019-05-22 14:32:53 12.5x12.5 deg
12 257.088 47.4065 2019-05-22 14:20:44 2019-05-22 14:32:53 12.5x12.5 deg
11 255.657 35.1801 2019-05-22 14:04:56 2019-05-22 14:32:53 12.5x12.5 deg
10 240.333 35.0506 2019-05-22 14:11:49 2019-05-22 14:32:53 12.5x12.5 deg

The covering map is available at:
http://cmm.svom.cn/gwpub/O3/S190521g/S190521g_GWAC.png
(user:svomo3 pwd:gwo3)

The first image was taken ~9.4 hours after the event trigger time. The
weather conditions were partly cloudy during the two consecutive days
of observations. A 3 sigma limiting magnitude of about 16 mag in R band
is typically obtained in our single frames.
No credible new source is detected by our online pipeline.
A more detailed image analysis including co-addition is ongoing with
our offline pipeline to search for faint transient candidates.

D. Turpin (NAOC), N. Dagoneau (CEA/AIM), L.P. Xin (NAOC),
X.H. Han (NAOC), J.Y. Wei (NAOC), C. Wu (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. 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), P.P. Zhang (NAOC),
R.S. Zhang (NAOC), E.W. Liang (GXU), X.G. Wang (GXU), Z.G. Dai (NJU),
X.Y. Wang (NJU), Y.G. Yang (HBNU), J.R. Mao (YNAO), B. Cordier (CEA/AIM),
S. Basa (CNRS/LAM), J.L. Atteia (UPS/IRAP), D. G�tz (CEA/AIM),
A. Claret (CEA/AIM), N. Leroy (CNRS/LAL), C. Lachaud (CNRS/APC), 
E. Le Floc'h (CEA/AIM), S.N. Zhang (IHEP), B.B. Wu (IHEP),
report on behalf of the SVOM Ground Follow-up Group:


We observed 4 sky regions to cover the initial skymap of the 
LIGO/Virgo trigger S190521g (GCN24621
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 ), with the SVOM/GWAC-F30 
telescope operated by Huaibei Normal University and NAOC, CAS 
at Xinglong Observatory, China. 
The SVOM/GWAC-F30 is equipped with Standard Johnson filters
and 3Kx3K FLI CCD (FOV~1.8x1.8 degree). The GWAC-F30 is using
tiling observation strategy. The tiles are calculated to cover
the most probable regions of the 90% localization area given in the
GW probability skymap. Several images with a single exposure of 60s
time in R band are taken for each tile.
The 4 tile coordinates and the observation periods are listed below:

# Ra[hms] Dec[dms] start-obs[UTC] Total_exp[s] N_image R_lim
1 12:33:04.799 +28:03:00.00 2019-05-21T13:53:59.727 300.0 5 16.82
2 16:40:40.800 +45:03:00.00 2019-05-21T14:02:19.437 300.0 5 16.33
3 16:41:33.601 +46:45:00.00 2019-05-21T13:19:33.245 300.0 5 16.38
4 16:50:12.239 +45:03:39.96 2019-05-21T13:16:11.066 420.0 7 15.75

The covering map is available at:
http://cmm.svom.cn/gwpub/O3/S190521g/S190521g_GWAC-F30.png
(user:svomo3 pwd:gwo3)

The first image was taken ~10.8 hours after the event trigger time. The
weather conditions were partly cloudy during the night. 
No credible new source is detected by our online pipeline.
A more detailed image analysis is in progress with our offline pipeline
to search for any fainter transient candidate.

A. Anumarlapudi (IITB), D. Saraogi (IITB), Aarthy E. (PRL), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (TIFR), S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

We have carried a search for X-ray candidates in Astrosat CZTI data in a 100 sec window around the trigger time of the BBH merger event S190521g (UTC 2019-05-21 03:02:29.000, GraceDB event). CZTI is a coded aperture mask instrument that has considerable effective area for about 29% of the entire sky, but is also sensitive to brighter transients from the entire sky. At the time of merger, Astrosat's nominal pointing is (RA=201.27, DEC=-43.09), which is 63.08 deg away from the maximum probability location. In time a interval of 100 sec around the event, 70% of the sky locations with the inclusion of maximum probability location are visible and not occulted by Earth in satellite's frame and the rest 30% are occulted.  

CZTI data were de-trended to remove orbit-wise background variation. We then searched data from three of the four independent, identical quadrants to look for coincident spikes in the count rates. Searches were undertaken by binning the data in 0.1s, 1s, and 10s respectively. Statistical fluctuations in count rates were estimated by using data from 10 (+-5) neighbouring orbits. We selected confidence levels such that the probability of a false trigger in a 1000 sec window is 10^-4.We do not find evidence for any hard X-ray transient in this window, in the CZTI energy range of 20-200 keV.

We convert our count rates into flux by assuming that the source spectrum is a power law with alpha = -1.0. We use a detailed mass model of the satellite to calculate the instrument response for every htm grid point that fall in 90% LIGO localization region and calculate flux limit in that direction. We get the following upper limits for source flux in the 20-200 keV band by taking a probability weighted mean of flux limit and are reported here :  

0.1 s: flux limit= 2.7 e-6 ergs/cm^2/s 
1.0 s: flux limit= 9.0 e-6 ergs/cm^2/s 
10.0 s: flux limit= 1.2 e-5 ergs/cm^2/s

We note that AstroSat was in the South Atlantic Anomaly at the instant of S190521r, hence no data are available for this event.


CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.