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GCN Circular 31176

Subject
GRB 211206A: Swift/BAT-GUANO detection outside the coded FOV
Date
2021-12-07T02:42:06Z (2 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 detected a rate increase onboard (trigger ##1088092) but did
not localize GRB 211206A (T0: 2021-12-06T19:51:10 UTC, AGILE/MCAL GCN
31175, CALET trig #1322855382).

The CALET 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
[-45,+45] 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 74.6 in a
4.096 s analysis time bin.
Estimated T90 in the detector is 6.6 +/- 0.2 s (15-350 keV).

NITRATES results strongly prefer an origin for the burst coming from
outside the coded FOV, with DeltaLLHOut of -55.5.

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/
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