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GCN Circular 25403

Subject
IceCube-190819A: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
Date
2019-08-19T19:53:39Z (5 years ago)
From
Sandro Mereghetti at IASF-Milano/INAF <sandro.mereghetti@inaf.it>
Sergey Molkov (IKI Moscow, Russia), Sandro Mereghetti (INAF IASF-Milano,
Italy),
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)

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

Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed a
search for a prompt gamma-ray counterpart of the   high-energy neutrino
candidate event IceCube-190819A (GCN 25402).

At the time of the event (2019-08-19 17:34:24 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 64 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(16% of optimal) response of ISGRI, strongly suppressed (26% of
optimal) response of IBIS/Veto, and somewhat suppressed (47% 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]) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 3.5e-07 erg/cm^2 (within the
50% probability containement 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 ~3.6e-07 (1.3e-07)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

We report for completness and in order of FAP, all excesses identified
in the search region. We find: 5 likely background excesses:

scale | T | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
3.75 | -114 | 3.9 | 2.64 +/- 0.604 +/- 0.819 | 0.11
5 | -95.2 | 3.5 | 1.94 +/- 0.523 +/- 0.602 | 0.148
0.1 | -2.52 | 3.1 | 1.19 +/- 0.374 +/- 0.367 | 0.499
0.15 | -13.8 | 3.6 | 1.12 +/- 0.305 +/- 0.346 | 0.581
0.15 | -18.3 | 3.7 | 1.15 +/- 0.305 +/- 0.357 | 0.626

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
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