GCN Circular 39183
Subject
LIGO/Virgo/KAGRA S250206dm: Upper limits from Fermi-GBM Observations
Date
2025-02-07T02:04:13Z (4 days ago)
From
oindabimukherjee@gmail.com
Via
Web form
O. Mukherjee (USRA) and R. Hamburg (USRA) report on behalf of the Fermi-GBM Team:
For S250206dm (GCN 39175; GCN 39178) and using the updated Bilby skymap, Fermi-GBM was observing 35.7% 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 S250206dm. 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=24.7, Dec=-4.2 with a radius of 67.9 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: 1.5 2.4 5.1
1.024 s: 0.44 0.72 1.3
8.192 s: 0.08 0.17 0.31
Assuming the median luminosity distance of 358.7 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: 0.71 1.02 2.95
1.024s: 0.09 0.14 0.47
8.192s: 0.02 0.02 0.04