GCN Circular 31541
Subject
GRB 220131B: Swift/BAT-GUANO detection outside the coded FOV
Date
2022-02-01T18:46:38Z (3 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay
(UAlabama), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 220131B onboard (T0: 2022-01-31T01:09:16.7
UTC, GECAM GCN 31534).
The GECAM notice, distributed in near real-time, triggered the Swift
Mission Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert
Telescope (BAT) to save 90 seconds of BAT event-mode data from [-50,+150]
seconds around the time of the burst. All the requested event mode data was
delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu,
arXiv:2111.01769), detects the burst with a sqrt(TS) of 9.2 in a 2.048 s
analysis time bin.
NITRATES results are consistent with a burst coming from outside the coded
FOV, with DeltaLLHOut of 1.9. The best fit sky position from NITRATES is
consistent with the GECAM localization within the stated error (GCN 31534).
See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions
and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/