TITLE:   GCN CIRCULAR
NUMBER:  31633
SUBJECT: GRB 220222A: Swift/BAT-GUANO detection outside the coded FOV
DATE:    22/02/22 14:18:17 GMT
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 220222A onboard (T0:
2022-02-22T02:21:17 UTC, Fermi/GBM GCN 31630, CALET trigger
#1329531683).

The Fermi 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 17.2 in a
2.048 s analysis time bin.
The observed duration of the burst is ~5 s.

NITRATES results are consistent with a burst coming from outside the
coded FOV, with DeltaLLHOut of -7. The best fit out of FoV location is
consistent with the Fermi/GBM localization (GCN 31630).

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/