GRB 220624A: Swift/BAT-GUANO detection outside the coded FOV
Abstract
Swift/BAT did not localize GRB 220624A onboard (T0: 2022-06-24T02:58:35 UTC, Fermi/GBM GCN 32256, CALET trig # 1340074490, AGILE GCN 32259,32261). The Fermi/GBM and CALET 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), detects the burst with a sqrt(TS) of 75 in a 16.384 s analysis time bin. The burst episode as seen by BAT is ~50 s long. NITRATES results indicate a burst coming from outside of the coded FoV, with DeltaLLHOut of -427. The NITRATES maximum likelihood sky position is consistent with the Fermi/GBM localization region. See Section 9.1 and Figure 20 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/
- Publication:
-
GRB Coordinates Network
- Pub Date:
- June 2022
- Bibcode:
- 2022GCN.32263....1T