GCN Circular 40955
Subject
LIGO/Virgo/KAGRA S250704ab: Upper limits from Fermi-GBM Observations
Date
2025-07-04T14:59:46Z (2 days ago)
From
Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>
Via
Web form
C. de Barra (UCD) reports on behalf of the Fermi-GBM Team:
For S250704ab (GCN 40935) and using the initial bayestar skymap, Fermi-GBM was observing 100.0% 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 S250704ab. 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=355.2, Dec=-25.3 with a radius of 68.0 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: 3.2 4.7 8.2
1.024 s: 0.97 1.3 2.4
8.192 s: 0.34 0.39 0.68
Assuming the median luminosity distance of 536 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: 0.17 0.23 0.66
1.024s: 0.05 0.06 0.19
8.192s: 0.02 0.02 0.05