Jamie A. Kennea (PSU), Gayathri Raman (PSU), Aaron Tohuvavohu (U
Toronto), James DeLaunay (UAlabama) report:
Swift/BAT did not localize GRB 220420A onboard (T0:
2022-04-20T03:54:31.9 UTC, CALET trig #1334461972, INTEGRAL/SPI-ACS
The CALET and INTEGRAL 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 108 seconds of BAT event-mode data from
[-45,+63] 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 65.8 in a
16.384 s analysis time bin.
The burst episode as seen by BAT is ~60s long.
NITRATES results strongly indicate a burst coming from outside the
coded FoV, with DeltaLLHOut of -489.
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/