[vsnet-grb-info 22629] LIGO/Virgo S190602aq: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24728
SUBJECT: LIGO/Virgo S190602aq: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
DATE:    19/06/03 08:50:54 GMT
FROM:    Francesca Onori at INAF/IAPS  <francesca.onori at inaf.it>

F. Onori (IAPS-Roma, Italy),
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 S190602aq
(GCN 24717).

At the time of the event (2019-06-02 17:59:27 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 128 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (3.9% of optimal) response of ISGRI, somewhat suppressed
(56% of optimal) response of IBIS/Veto, and strongly suppressed (29%
of optimal) response of SPI-ACS.

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), 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 3.8e-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=-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 ~3.7e-07 (1.2e-07)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

-- 
Dr. Francesca Onori
Postdoctoral Researcher
IAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy
e-mail: francesca.onori at inaf.it
Tel: +39 06 45488128