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GCN Circular 32823

Subject
GRB 221022B: Swift/BAT-GUANO detection outside the coded FOV
Date
2022-10-24T00:22:00Z (a year ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
Gayathri Raman (PSU),  Aaron Tohuvavohu (U Toronto), James DeLaunay
(UAlabama), Jamie A. Kennea (PSU), Tyler Parsotan (GSFC/UMBC) report:

Swift/BAT did not localize GRB 221022B onboard (T0:
2022-10-22T22:55:48 UTC, Fermi/GBM GCN 32820, AGILE GCN 32822).

The Fermi 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 44.9 in a
16.384 s analysis time bin.

NITRATES results are consistent with a burst coming from outside the
FOV, with DeltaLLHOut of -17. The best fit sky location is consistent
with the Fermi/GBM position (GCN 32820).

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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