GCN Circular 31334

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

Swift/BAT did not localize GRB 211229A onboard (T0:
2021-12-29T03:29:15 UTC, Fermi/GBM GCN 31329
Not found
 
 
, GECAM GCN 31331
Not found
 
 
).

The Fermi 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
Not found
 
 
), confidently detects the burst in a 16.384 s
analysis time bin with a sqrt(TS) of 50.
Estimated duration in the detector is greater than 60 s.

A confident arcminute localization is found with DeltaLLHOut of 567
and a DeltaLLHPeak of 269.

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

The BAT position is
RA, Dec = 295.044, 23.133  deg which is
   RA(J2000)  = 19h 40m 10.56s
   Dec(J2000) =  +23d 07��� 58���
with an estimated uncertainty of 4 arcmin.

XRT and UVOT follow-up has been requested.
Results of follow-up observations will be reported in future circulars.

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/