TITLE: GCN CIRCULAR NUMBER: 36793 SUBJECT: LIGO/Virgo/KAGRA S240629by: Upper limits from Fermi-GBM Observations DATE: 24/06/30 02:18:52 GMT FROM: Vidushi Sharma at NASA GSFC/UMBC vidushi.sharma@nasa.gov
V. Sharma (NASA GSFC/UMBC) reports on behalf of the Fermi-GBM Team:
For S240629by (GCN 36784) and using the initial bayestar skymap, Fermi-GBM was observing 17.8% 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 S240629by. 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=30.0, Dec=-25.6 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: 2.1 3.5 7.2 1.024 s: 0.7 1.1 2.1 8.192 s: 0.3 0.5 0.9
Assuming the median luminosity distance of 1205 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: 0.6 0.8 2.9 1.024s: 0.2 0.3 0.8 8.192s: 0.1 0.1 0.4
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