GCN Circular 26187

C. Ferrigno, V. Savchenko (ISDC/UniGE, Switzerland)
Sergey Molkov (IKI, Russia)
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 a combination of the INTEGRAL all-sky detectors:
SPI/ACS, IBIS/Veto, and IBIS (following [1]) we have performed a search 
for a prompt
gamma-ray counterpart of S191105e (GCN 26182
Not found
 
 
).

At the time of the event (2019-11-05 14:35:21 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 93 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(9.1% of optimal) response of ISGRI, strongly suppressed (27% of
optimal) response of IBIS/Veto, and near-optimal (79% 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 2.3e-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 ~2e-07 (5.2e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

For the mean reported distance 1168 Mpc this corresponds to the
limit on the total isotropic equivalent energy in 1 s of 3.7e+49 erg
for the short GRB spectrum and for a long GRB spectrum isotropic
equivalent luminosity in 1 s (8 s) of 2.7e+49 erg/s (8.5e+48 erg/s)

We find: 4 likely background
excesses that we report for completeness and in order of FAP
in the search region of SPI-ACS data.

scale | T | S/N | luminosity ( x 1e+49 erg/s) | FAP
13.8 | 167 | 3.4 | 12.2 +/- 5 +/- 7.36 | 0.113
0.15 | -2.86 | 3.1 | 12.2 +/- 4.85 +/- 7.37 | 0.358
2.55 | -295 | 3.6 | 3.32 +/- 1.17 +/- 2 | 0.701
0.5 | -168 | 4.3 | 9.36 +/- 2.65 +/- 5.66 | 0.797

Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.


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