TITLE:   GCN CIRCULAR
NUMBER:  33220
SUBJECT: GRB 230124A: Swift/BAT-GUANO detection outside the coded FOV
DATE:    23/01/25 02:49:23 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

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

Swift/BAT did not localize GRB 230124A onboard (T0:
2023-01-24T15:18:46 UTC, Fermi/GBM GCN 33215).

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 2022, ApJ,
941, 169), detects the burst with a sqrt(TS) of 9.5 in a 4.096 s
analysis time bin.

NITRATES results are consistent with a burst coming from outside the
FOV, as suggested by the Fermi/GBM localization.

See Section 9.1 and Figures 10 and 17 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/