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GCN Circular 36241

LIGO/Virgo/KAGRA S240422ed: Upper limits from Fermi-GBM Observations
2024-04-23T03:21:42Z (3 months ago)
Oliver J Roberts at USRA/NASA <>
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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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