GCN Circular 20933

R. Sunyaev (IKI, Russia) on behalf of the INTEGRAL group:
R. Krivonos (IKI, Russia),
V. Savchenko (ISDC, University of Geneva, CH),
A. Lutovinov, S. Grebenev (IKI, Russia),
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),
J. Chenevez, S. Brandt (DTU - Denmark),
R. Diehl (MPE-Garching, Germany) ,
L. Hanlon (UCD, Ireland), P. Laurent (APC, Saclay/CEA, France),
  J.P. Roques (CESR, France), P. Ubertini (IAPS-Roma, Italy)

We report on serendipitous follow-up INTEGRAL observations of the part
of the LIGO localization area carried out several hours after the
trigger for the LIGO/Virgo burst candidate G277583.  During these
observations (from 2017-03-14 11:21:32 to 2017-03-16 09:26:32 with the
total net exposure of 120 ks) the satellite monitored the Galactic
Center region. The total LIGO localization probability in the region
observed by ISGRI/IBIS is 19.5% for cWB localization and 11.5% for the
recommended combined cWB_plus_LIB map.

No new sources were found in the IBIS field of view (FOV) during these
observations with 3-sigma upper limits of 5.1 mCrab (6.3?-11
erg/s/cm2) in the fully coded FOV of IBIS and 4.2 mCrab (5.1?-11
erg/s/cm2) at the peak sensitivity of ISGRI in the 20-60 keV energy
band.  A 3-sigma upper limit of 50 mCrab in the 3-10 keV energy band
for any new sources was derived from the JEM-X instrument as well,
which covered <3% of the LIGO probability area.

During these observations INTEGRAL/SPI-ACS and IBIS/Veto performed
nearly continuous monitoring of the whole LIGO localization region
with an approximate 1-s peak flux sensitivity of 9e-7 erg/cm2
(assuming a typical short GRB spectrum described by a cutoff powerlaw
model with alpha=-0.5 and E_peak=500 keV). No GRB-like events have
been detected.

Finally, we also inspected earlier INTEGRAL observations of the same
region, which finished about 15 minutes before the LIGO trigger (from
2017-03-11 19:34:35 to 2017-03-13 22:25:18 with the total net exposure
of 113 ks). Also in this time frame did we not find any new sources or
unusual events, with approximately the same upper limits.