[vsnet-grb-info 28443] Fermi GBM Sub-Threshold Detection of GRB 210725B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30546
SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 210725B
DATE:    21/07/29 15:10:40 GMT
FROM:    Cori Fletcher at USRA  <cfletcher at usra.edu>

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team:

Swift-BAT detected GRB 210725B at 12:00:48 UT (GCN 30508). 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 a transient source at this time.

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 false alarm rate of 2.6e-05 Hz and a location consistent with
the Swift-BAT event, using the standard search protocol with a S/N of 9.
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