GCN Circular 28445
Subject
Fermi-GBM Sub-Threshold Detection of GRB 200917A
Date
2020-09-17T20:40:02Z (4 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 200917A at 03:52:28 UT (Sonbas et al. 2020, GCN 28435).
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 also identified no counterparts.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like
signals, was run from +/-30 s around BAT trigger time.
A transient source was identified whose most significant timescale according to
the automated search is 4.096 s, with a log likelihood ratio of 21. This timescale
corresponds to the first peak in the lightcurve, occurring -11 seconds before the
BAT trigger time. The full light curve consists of multiple peaks spanning from
approximately 11 seconds before to 10 seconds after the BAT trigger time.
The location is consistent with that from Swift-BAT.
The spectrum is consistent with a "normal" GRB template
(Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3).
[1] Goldstein et al. 2019 arXiv:1903.12597