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GCN Circular 31943

Subject
GRB 220423A: Swift/BAT-GUANO detection outside the coded FOV
Date
2022-04-24T02:21:14Z (2 years 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), report:

Swift/BAT did not localize GRB 220423A onboard (T0: 2022-04-23T14:14:10
UTC, CALET trig #1334758343, INTEGRAL/SPI-ACS trig #9870, AGILE GCN 31938).

Happy Birthday AGILE!

The CALET and INTEGRAL 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 by this notice, GUANO sent a command to the Swift Burst Alert
Telescope (BAT) to save 92 seconds of BAT event-mode data from [-46,+46]
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 139 in a 8.192 s
analysis time bin.

The burst episode as seen by BAT is ~20s long.

NITRATES results strongly indicate a burst coming from outside the coded
FoV, with DeltaLLHOut of -734.

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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