GCN Circular 31047
Subject
GRB 211105A: Swift/BAT-GUANO detection outside the coded FOV
Event
Date
2021-11-06T02:15:09Z (5 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:
Swift/BAT did not trigger on GRB 211105A (T0: 2021-11-05T04:35:20.2
UTC, GECAM-B GCN #31046).
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 200 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 16 in a 16.384
s analysis time bin. This is the maximum test duration of the search
pipeline. The full burst duration in the detector is greater than 60
s.
NITRATES prefers an origin for this burst coming from outside the
coded FOV, with DeltaLLHOut of -4.
An out of FOV origin is consistent with the GECAM localization.
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/