TITLE: GCN CIRCULAR
NUMBER: 24925
SUBJECT: LIGO/Virgo S190630ag: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
DATE: 19/06/30 21:30:10 GMT
FROM: Alexis Coleiro at APC/U. Paris Diderot
Alexis Coleiro (APC, France), F. Onori (IAPS-Roma, Italy)
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
S. Mereghetti (INAF IASF-Milano, Italy)
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 S190630ag (GCN 24922).
At the time of the event (2019-06-30 18:52:05 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 150 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (4% of optimal) response of ISGRI, near-optimal (94% of optimal) response of IBIS/Veto, and strongly suppressed (24% 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 1.9e-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 ~1.6e-07 (6.9e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.
For the mean reported distance of 1059.0 Mpc, this corresponds to the limit on the total isotropic equivalent energy in 1 s of 2.5e+49 erg for the short GRB spectrum and for a long GRB spectrum isotropic equivalent luminosity in 1 s (8 s) of 2.1e+49 erg/s (9.3e+48 erg/s).
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