GCN Circular 33982
Subject
GRB 230616A: Swift/BAT-GUANO detection of a short burst outside the coded FOV
Date
2023-06-17T03:52:13Z (a year ago)
From
Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>
Aaron Tohuvavohu (U Toronto), James DeLaunay (U Alabama), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU) report:
Swift/BAT did not localize GRB 230616A onboard (T0: 2023-06-16T20:37:56.8 UTC, INTEGRAL trig 10287)
The INTEGRAL 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 90 seconds of BAT event-mode data from [-45,+45] 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 29.2 in a 0.128 s analysis time bin.
NITRATES results are consistent with a burst coming from outside the FOV, with DeltaLLHOut of -1.
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/