GCN Circular 28663
Subject
Fermi GBM Sub-Threshold Detection of GRB 201015A
Event
Date
2020-10-16T21:25:33Z (5 years ago)
From
Cori Fletcher at USRA <cfletcher@usra.edu>
C. Fletcher (USRA) and P. Veres (UAH) report on behalf of the Fermi-GBM Team:
Swift-BAT detected GRB 201015A at 22:50:13 UT (GCN 28632). 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 was run from +/-30 s around the BAT trigger time. A transient source was
identified whose most significant timescale according to the automated search is 1.024 s,
with a log likelihood ratio of 76 and a location consistent with the Swift-BAT event.
The time-averaged spectrum from T0-0.256 s to T0+0.896 s is adequately fit by a
Band function with Epeak = 14 +/- 6 keV, alpha = -1.0 (fixed), and beta = -2.40
+/- 0.21. Because the peak energy is close to the low energy threshold of GBM,
the low energy photon index is unconstrained. We fix it to the median value of
the GBM GRB sample, however it has no significant effect on the values for Epeak and beta.
The event fluence (10-1000 keV) in this time interval is(2.25 +/- 0.38)E-07 erg/cm^2.
T0 here is 2020-10-15T22:50:13.22 UT = 624495018.22 (MET)
[1] Goldstein et al. 2019 arXiv:1903.12597