GRB 230822A: Swift/BAT-GUANO detection of a burst

Swift/BAT did not localize GRB 230822A onboard (T0: 2023-08-22T23:48:54.40 UTC, Fermi GBM Trig 714440939, GCN 34521). 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 9.7 in a 1.024 s analysis time bin, starting at T0 - 1.792 s. NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a DeltaLLHOut of 7.7. 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/