GCN Circular 31291
Subject
Fermi GBM Sub-Threshold Detection of GRB 211221A
Date
2021-12-23T15:05:00Z (2 years ago)
From
Cori Fletcher at USRA <cfletcher@usra.edu>
C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team:
Swift-BAT detected GRB 211221A at 20:48:40 UT (GCN 31273). There was no
Fermi-GBM onboard trigger around 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 S/N of 21, 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.
[1] Goldstein et al. 2019 arXiv:1903.12597