[vsnet-grb-info 24829] LIGO/Virgo S200129m: No counterpart candidates in INTEGRAL SPI-ACS prompt observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26928
SUBJECT: LIGO/Virgo S200129m: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
DATE:    20/01/29 08:15:41 GMT
FROM:    Francesca Onori at INAF/IAPS  <francesca.onori at inaf.it>

LIGO/Virgo S200129m: No counterpart candidates in INTEGRAL SPI-ACS
prompt observationFrancesca Onori (IAPS, Italy), Sergey Molkov (IKI, Moscow)
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-collaborationUsing
INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of S200129m (GCN 26926).At the
time of the event (2020-01-29 06:54:58 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 112 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (5% of optimal) response of ISGRI, somewhat
suppressed (44% of optimal) response of IBIS/Veto, and strongly
suppressed (37% of optimal) response 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 4.5e-07 erg/cm^2 (within the
50% probability containment region of the source localization) for a
burst lasting less than 1s 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 300s 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 ~4.1e-07 (1.3e-07)
erg/cm^2/s at 1s (8s) time scale in 75-2000 keV energy range.For the mean
reported distance 908.0 Mpc this corresponds to the limit
on the total isotropic equivalent energy in 1s of 4.5e+49 erg for
the short GRB spectrum and for a long GRB spectrum isotropic
equivalent luminosity in 1s (8s) of 3.7e+49 erg/s (1.3e+49 erg/s)We report
for completeness and in order of FAP, all excesses
identified in the search region. We find: 1 possibly associated
excess:T-T0 | scale | S/N | luminosity ( x 1e+49 erg/s) | FAP
-1.52 | 0.1 | 4.2 | 20.7 +/- 4.89 +/- 6.38 | 0.03944 likely background
excesses:T-T0 | scale | S/N | luminosity ( x 1e+49 erg/s) | FAP
-16.2 | 1.95 | 3.4 | 3.88 +/- 1.09 +/- 1.2 | 0.0685
-38.6 | 0.5 | 3.8 | 8.01 +/- 2.16 +/- 2.48 | 0.344
25.7 | 0.15 | 4.4 | 17.8 +/- 3.98 +/- 5.51 | 0.373
-121 | 0.4 | 4.2 | 10.3 +/- 2.42 +/- 3.18 | 0.775Note 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

-- 
Dr. Francesca Onori
Postdoctoral Researcher
IAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy
e-mail: francesca.onori at inaf.it
Tel: +39 06 45488128