GCN Circular 34860
Subject
LIGO/Virgo/KAGRA S231020ba: Upper limits from Fermi-GBM Observations
Date
2023-10-20T19:40:41Z (6 months ago)
From
sumanbala2210@gmail.com
Via
Web form
S. Bala (USRA) reports on behalf of the Fermi-GBM Team:
For S231020ba (GCN 34852) and using the initial bayestar skymap, Fermi-GBM was observing 25.4% 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 S231020ba. 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=121.7, Dec=23.2 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: 3.3 4.0 6.6
1.024 s: 1.3 1.5 2.1
8.192 s: 0.4 0.4 0.7
Assuming the median luminosity distance of 1110.8 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: 0.8 0.8 2.3
1.024s: 0.3 0.3 0.7
8.192s: 0.1 0.1 0.2