TITLE:   GCN CIRCULAR
NUMBER:  31174
SUBJECT: GRB 211204C: Swift/BAT-GUANO detection outside the coded FOV
DATE:    21/12/05 15:40:48 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:

Swift/BAT did not successfully trigger on GRB 211204C (T0:
2021-12-04T21:37:00 UTC, Fermi/GBM GCN 31171, GECAM GCN 31173,
INTEGRAL/SPI-ACS trig #9552).

The Fermi/GBM, INTEGRAL, and GECAM 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 116.1 in a
8.192 s analysis time bin.
Estimated T90 in the detector is 19.5 +/- 0.1 s (15-350 keV).

NITRATES strongly prefers an origin for the burst coming from outside
the coded FOV, with DeltaLLHOut of -520.
An out of FOV origin is consistent with the Fermi/GBM and GECAM localizations.

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/