[vsnet-grb-info 23020] LIGO/Virgo S190720a: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation

Sat Jul 20 16:44:04 JST 2019

TITLE:   GCN CIRCULAR
NUMBER:  25119
SUBJECT: LIGO/Virgo S190720a: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
DATE:    19/07/20 07:42:37 GMT
FROM:    Maeve Doyle at U College Dublin, Ireland  <maeve.doyle.1 at ucdconnect.ie>

<html><head></head><body dir=3D"auto" style=3D"word-wrap: break-word; -webk=
it-nbsp-mode: space; line-break: after-white-space;"><div class=3D"ApplePla=
inTextBody">Maeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Russia)<b=
r>V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)<br>J. Rodi (IAPS-Roma=
, Italy)<br>A. Coleiro (APC, France)<br>S. Mereghetti (INAF IASF-Milano, It=
aly)<br><br>on behalf of the INTEGRAL multi-messenger collaboration:<br>htt=
ps://www.astro.unige.ch/cdci/integral-multimessenger-collaboration<br><br>U=
sing combination of INTEGRAL all-sky detectors (following [1]):<br>SPI/ACS,=
 IBIS/Veto, and IBIS we have performed a search for a prompt<br>gamma-ray c=
ounterpart of S190720a (GCN 25115).<br><br>At the time of the event (2019-0=
7-20 00:08:36 UTC, hereafter T0),<br>INTEGRAL was operating in nominal mode=
. The peak of the event<br>localization probability was at an angle of 112 =
deg with respect to<br>the spacecraft pointing axis. This orientation impli=
es strongly<br>suppressed (7% of optimal) response of ISGRI, strongly suppr=
essed (31%<br>of optimal) response of IBIS/Veto, and near-optimal (70% of o=
ptimal)<br>response of SPI-ACS.<br><br>The background within +/-300 seconds=
 around the event was rather<br>stable (excess variance 1.2).<br><br>We hav=
e performed a search for any impulsive events in INTEGRAL SPI-<br>ACS (as d=
escribed in [2]), IBIS, and IBIS/Veto data.<br><br>We do not detect any sig=
nificant counterparts and estimate a 3-sigma<br>upper limit on the 75-2000 =
keV fluence of 1.8e-07 erg/cm^2 (within the<br>50% probability containment =
region of the source localization) for a<br>burst lasting less than 1 s wit=
h a characteristic short GRB spectrum<br>(an exponentially cut off power la=
w with alpha=3D-0.5 and Ep=3D600 keV)<br>occurring at any time in the inter=
val within 300 s around T0. For a<br>typical long GRB spectrum (Band functi=
on with alpha=3D-1, beta=3D-2.5, and<br>Ep=3D300 keV), the derived peak flu=
x upper limit is ~1.5e-07 (5.6e-08)<br>erg/cm^2/s at 1 s (8 s) time scale i=
n 75-2000 keV energy range.<br><br>For the mean reported distance 1071.0 Mp=
c this corresponds to the<br>limit on the total isotropic equivalent energy=
 in 1 s of 2.5e+49 erg<br>for the short GRB spectrum and for a long GRB spe=
ctrum isotropic<br>equivalent luminosity in 1 s (8 s) of 2.1e+49 erg/s (7.7=
e+48 erg/s)<br><br><br>All results quoted are preliminary.<br><br>This circ=
ular is an official product of the INTEGRAL Multi-Messenger<br>team.<br><br=
>[1] Savchenko et al. 2017, A&A 603, A46 <br>[2] Savchenko et al. 2012,=
 A&A 541A, 122S<br></div></body></html>