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GCN Circular 31696

Subject
Fermi GBM Sub-Threshold Detection of GRB 220305A
Date
2022-03-06T16:47:37Z (2 years ago)
From
Joshua Wood at MSFC/Fermi-GBM <joshua.r.wood@nasa.gov>
J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM Team:

Swift-BAT detected GRB 220305A at 16:13:08 UT on 05 March, 2022 (Caputo
et al. GCN 31684). There was no Fermi-GBM onboard trigger around the
time of the event.
 
An automated, blind search for short gamma-ray bursts below the onboard
triggering threshold in Fermi-GBM identified no counterparts.

The GBM targeted search [1], the most sensitive, coherent search for
GRB-like signals identified a transient most significantly on the 8.192 s
timescale, with a location consistent with the Swift-BAT event and
a signal-to-noise ratio of 17.8, using the standard search protocol.
The GBM targeted search event was found with the highest
significance with a "normal" spectrum (Band function with
Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.

This analysis is preliminary.

[1] Goldstein et al. 2019 arXiv:1903.12597

Note: Fermi-GBM also detected GRB 220305B at 11:33:20.48 UT on 05 March 2022
which was erroneously named GRB 220305A at the time of its initial publication
(GCN 31689, 31690). GRB 220305B is a different burst than the one
described here.
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