GCN Circular 31487
Subject
Fermi GBM Sub-Threshold Detection of GRB 220117A
Date
2022-01-18T16:53:23Z (2 years ago)
From
Peter Veres at UAH <veresp@gmail.com>
P. Veres (UAH)
reports on behalf of the Fermi-GBM Team:
���Swift-BAT detected GRB 220117A at T0=2022-01-17T16:18:51.5 UT
(Melandri et al, GCN 31466). There was no Fermi-GBM onboard trigger
around the event.
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 search is 4.096 s with a false alarm rate of 1.9e-5 Hz, and a
location consistent with the Swift-BAT event, using the standard search
protocol with a S/N of 11.4. The GBM targeted search event was found with
the highest significance with a ���soft��� spectral template (Band
function with Epeak = 70 keV, alpha = -1.9, beta = -3.7).
The GBM light curve consists of multiple overlapping pulses. The
time-averaged spectrum from T0 + 11.7 s to T0 + 69.0 s is best fit by
a power law function with an exponential high-energy cutoff. The
power law index is -1.39 +/- 0.20 and the cutoff energy, parameterized
as Epeak, is 40.0 +/- 4.8 keV.
The event fluence (10-1000 keV) in this time interval for the best fitting
model is (2.40 +/- 0.17)E-6 erg/cm^2. Using the redshift z=4.961 reported
by Palmerio et al. (GCN 31480), we derive an isotropic equivalent energy in
the 1-10,000 keV range of (1.56 +/- 0.11)E+53 erg.
This analysis is preliminary.
[1] Goldstein et al. 2019 arXiv:1903.12597
���