[vsnet-grb-info 25513] IceCube-200421A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27613
SUBJECT: IceCube-200421A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
DATE:    20/04/21 10:30:17 GMT
FROM:    Alexander Lutovinov at Space Research Inst.,IKI  <aal at iki.rssi.ru>

Alexander Lutovinov (IKI, Russia),  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 [1]):
SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt
gamma-ray counterpart of unknown (GCN 27612).

At the time of the event (2020-04-21 00:35:24 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 162 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (3.7% of optimal) response of ISGRI, near-optimal (85% of
optimal) response of IBIS/Veto, and strongly suppressed (38% of
optimal) response of SPI-ACS.

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

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 4.9e-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 ~5e-07 (9.2e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

We report for completeness and in order of FAP, all excesses
identified in the search region. We find: 2 possibly associated
excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
3.07 | 1.15 | 3.6 | 0.553 +/- 0.152 +/- 0.186 | 0.0163
40 | 9.5 | 3.5 | 2.09 +/- 0.526 +/- 0.703 | 0.033

2 likely background excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
-36.6 | 1.5 | 3.3 | 0.433 +/- 0.133 +/- 0.146 | 0.307
-119 | 0.35 | 4.6 | 1.25 +/- 0.277 +/- 0.419 | 0.668
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