GCN Circular 30125
Subject
Fermi GBM Sub-Threshold Detection of new Swift SGR J1555.2-5402
Date
2021-06-04T17:34:43Z (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 Swift SGR J1555.2-5402 at 09:45:46 UT (GCN 30120).
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 64 ms, with a false alarm rate
of 5.8e-05 Hz and a location consistent with the Swift-BAT event,
using the standard search protocol with a S/N of 6. The event was
found to be even more significant (S/N of 12) on the 8 ms timescale,
but an associated false alarm rate is currently not available on the
8 ms timescale. 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).
[1] Goldstein et al. 2019 arXiv:1903.12597