GCN Circular 35021
Subject
LIGO/Virgo/KAGRA S231113bw: Upper limits from Fermi-GBM Observations
Date
2023-11-14T03:11:36Z (6 months ago)
From
Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>
Via
Web form
P. Veres (UAH) reports on behalf of the Fermi-GBM Team:
"For S231113bw (GCN 35016) and using the initial bayestar skymap, Fermi-GBM was observing 37% of the localization probability at event time.
There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW trigger S231113bw. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.
Part of the LVK localization region is behind the Earth for Fermi, located at an RA=280.7, Dec=12.6 with a radius of 67.4 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard
------------------------------------
0.128 s: 1.2 2.0 4.3
1.024 s: 0.39 0.49 1.2
8.192 s: 0.097 0.15 0.35
Assuming the median luminosity distance of 1431 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^50 erg/s):
Timescale Soft Normal Hard
------------------------------------
0.128s: 0.46 0.68 2.5
1.024s: 0.15 0.17 0.69
8.192s: 0.037 0.051 0.20