TITLE: GCN CIRCULAR NUMBER: 36241 SUBJECT: LIGO/Virgo/KAGRA S240422ed: Upper limits from Fermi-GBM Observations DATE: 24/04/23 03:21:42 GMT FROM: Oliver J Roberts at USRA/NASA oliver.roberts@nasa.gov
O.J. Roberts (USRA/NASA-MSFC) reports on behalf of the Fermi-GBM Team:
For S240422ed (GCN 36240) and using the updated 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 S240422ed. 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.
No part of the LVK localization region is behind the Earth for Fermi, located at an RA= 08h 13m, Dec.= - 26d 38m with an area of 272 deg2. 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: 1.8 3.4 7.5 1.024 s: 0.6 0.9 2.4 8.192 s: 0.2 0.3 0.9
Assuming the median luminosity distance of 188.2 +/- 43.2 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^48 erg/s):
Timescale Soft Normal Hard ------------------------------------------ 0.128s: 1.16 2.05 7.42 1.024s: 0.37 0.54 2.37 8.192s: 0.11 0.20 0.84
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