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GCN Circular 30421

Subject
Fermi GBM Sub-Threshold Detection of GRB 210708A
Date
2021-07-08T16:52:18Z (3 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 210708A at 02:25:37 UT (GCN 30413). 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 4.096 s
timescale, with a false alarm rate of 1.7e-04 Hz and a location consistent with
the Swift-BAT event, using the standard search protocol with a S/N of 6.
The GBM targeted search event was found with the highest
significance with a "soft" spectrum (Band function with
Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB.

[1] Goldstein et al. 2019 arXiv:1903.12597
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