[vsnet-grb-info 21967] INTEGRAL observation of S190408an

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24066
SUBJECT: INTEGRAL observation of S190408an
DATE:    19/04/08 21:04:49 GMT
FROM:    Volodymyr Savchenko at ISDC,U of Geneve  <savchenk at in2p3.fr>

Volodymyr Savchenko, Carlo Ferrigno  (ISDC/UniGE, Switzerland)
James Rodi,  (IAPS-Roma, Italy)
Sandro Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration


Using INTEGRAL we have performed a search for a prompt gamma-ray
counterpart of S190408an.

At the time of the event (2019-04-08 18:18:02.29 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 115 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed response of IBIS, strongly suppressed response of
IBIS/Veto, and somewhat suppressed response of SPI-ACS.

The background within +/-300 seconds around the event was very stable.
We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2.5e-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 (8.1e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV
energy range.