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GCN Circular 26225

LIGO/Virgo S191110af: No counterpart candidates in INTEGRAL SPI-ACS, prompt observation
2019-11-11T04:59:34Z (5 years ago)
Sergey Molkov at Space Research Inst., Moscow <>
Sergey Molkov (IKI, Russia), Maeve Doyle (UCD, Ireland),
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:

Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of S191110af (GCN 26222).

At the time of the event (2019-11-10 23:06:44 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 105 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (6.1% of optimal) response of ISGRI, strongly suppressed
(22% of optimal) response of IBIS/Veto, and somewhat suppressed (59%
of optimal) respo nse 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 [2]) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2.8e-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 ~2.4e-07 (8e-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: 1 possibly associated

scale | T | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
0.1 | 0.877 | 3.6 | 1.14 +/- 0.312 +/- 0.357 | 0.0497

3 likely background excesses:

scale | T | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
0.2 | -31 | 3.7 | 0.832 +/- 0.22 +/- 0.261 | 0.735
0.95 | 185 | 3.8 | 0.385 +/- 0.1 +/- 0.121 | 0.853
0.65 | 63.2 | 3.4 | 0.413 +/- 0.121 +/- 0.13 | 0.953

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

All results quoted are preliminary.

This circular is an official product of the INTEGRAL Multi-Messenger

[1] Savchenko et al. 2017, A&A 603, A46
[2] Savchenko et al. 2012, A&A 541A, 122S

[GCN OPS NOTE(12nov19):  Per author's request, the "unknown" in the Subject-line
was replavced with "S191110af".]
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