[vsnet-grb-info 22281] LIGO/Virgo S190503bf: INTEGRAL prompt observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24380
SUBJECT: LIGO/Virgo S190503bf: INTEGRAL prompt observation
DATE:    19/05/03 21:22:44 GMT
FROM:    Sandro Mereghetti at IASF-Milano/INAF  <sandro.mereghetti at inaf.it>

James Rodi (IAPS-Roma, Italy),  Sandro Mereghetti (INAF IASF-Milano, Italy)
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland), A. Coleiro (APC,
France) on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration
report:

Using the 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 S190503bf
(GCN 24377).

At the time of the event (2019-05-03 18:54:04 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 120 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (5.7% of optimal) response of ISGRI, strongly suppressed
(28% of optimal) response of IBIS/Veto, and somewhat suppressed (64%
of optimal) response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.3).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in Savchenko et al. 2012, A&A 541A, 122S), 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 2.4e-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 ~2.1e-07 (8.4e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.