GCN Circular 24624

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.