TITLE: GCN CIRCULAR
NUMBER: 25119
SUBJECT: LIGO/Virgo S190720a: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
DATE: 19/07/20 07:42:37 GMT
FROM: Maeve Doyle at U College Dublin, Ireland
Maeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Russia),
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 [1]):
SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt
gamma-ray counterpart of S190720a (GCN 25115).
At the time of the event (2019-07-20 00:08:36 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 112 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (7% of optimal) response of ISGRI, strongly suppressed (31%
of optimal) response of IBIS/Veto, and near-optimal (70% of optimal)
response of SPI-ACS.
The background within +/-300 seconds around the event was rather
stable (excess variance 1.2).
We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]), IBIS, and IBIS/Veto data.
We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 1.8e-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=3D-0.5 and Ep=3D600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=3D-1, beta=3D-2.5, and
Ep=3D300 keV), the derived peak flux upper limit is ~1.5e-07 (5.6e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.
For the mean reported distance 1071.0 Mpc this corresponds to the
limit on the total isotropic equivalent energy in 1 s of 2.5e+49 erg
for the short GRB spectrum and for a long GRB spectrum isotropic
equivalent luminosity in 1 s (8 s) of 2.1e+49 erg/s (7.7e+48 erg/s)
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 OPS NOTE(20jul19): There was a format error caused by a copy-paste error
in the original submission. Per author's request, it has been manually
reconstructed in plain text here.]