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GCN Circular 32263

Subject
GRB 220624A: Swift/BAT-GUANO detection outside the coded FOV
Date
2022-06-24T18:45:57Z (2 years 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 220624A onboard (T0:
2022-06-24T02:58:35 UTC, Fermi/GBM GCN 32256, CALET trig # 1340074490,
AGILE GCN 32259,32261).

The Fermi/GBM and CALET 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 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 75 in a 16.384
s analysis time bin.
The burst episode as seen by BAT is ~50 s long.

NITRATES results indicate a burst coming from outside of the coded
FoV, with DeltaLLHOut of -427. The NITRATES maximum likelihood sky
position is consistent with the Fermi/GBM localization region.

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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