James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 220304A onboard (T0: 2022-03-04T05:28:58
UTC, Fermi/GBM GCN 31672).
The Fermi 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 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 49 in a 16.384
s analysis time bin, the longest time bin of the search.
The duration of the burst is at least 30 seconds.
NITRATES results indicate a burst coming from outside the coded FOV,
with DeltaLLHOut of -55. The best fit location is consistent with the
Fermi/GBM RoboBA (GCN 31672), and BALROG (GCN 31674) localizations.
See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and
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/