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GCN Circular 32984

Subject
GRB 221124A: Swift/BAT-GUANO detection
Date
2022-11-26T07:55:10Z (a year 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 221124A onboard (T0:
2022-11-24T02:00:24 UTC, CALET trig 1353290389, GECAM trig 79).

The CALET and GECAM notices, 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, 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 8 in a 1.024 s
analysis time bin.

NITRATES results, independently, are ambiguous with respect to whether
this burst originates from in or outside the BAT FOV.
The GECAM localization places this burst outside the contemporaneous BAT FoV.

See Section 9.1 and Figures 10 and 17 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/
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