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GCN Circular 31550

Subject
GRB 220203A: Swift/BAT-GUANO detection outside the coded FOV
Date
2022-02-05T00:28:41Z (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 220203A onboard (T0: 2022-02-03T21:15:39.8 UTC,
INTEGRAL #9677, IPN GCN 31549).

The INTEGRAL 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 14.6 in a 0.256 s
analysis time bin.

The duration of the burst is ~0.3 seconds.

NITRATES results are consistent with a burst coming from outside the coded
FOV, with DeltaLLHOut of 4. An out of FOV origin is consistent with the IPN
localization (GCN 31549).

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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