TITLE: GCN CIRCULAR NUMBER: 31334 SUBJECT: GRB 211229A: Swift/BAT-GUANO arcminute localization DATE: 21/12/29 14:16:59 GMT FROM: Aaron Tohuvavohu at U Toronto aaron.tohu@gmail.com
Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay (UAlabama), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 211229A onboard (T0: 2021-12-29T03:29:15 UTC, Fermi/GBM GCN 31329, GECAM GCN 31331).
The Fermi and GECAM 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), confidently detects the burst in a 16.384 s analysis time bin with a sqrt(TS) of 50. Estimated duration in the detector is greater than 60 s.
A confident arcminute localization is found with DeltaLLHOut of 567 and a DeltaLLHPeak of 269.
See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is RA, Dec = 295.044, 23.133 deg which is RA(J2000) = 19h 40m 10.56s Dec(J2000) = +23d 07′ 58″ with an estimated uncertainty of 4 arcmin.
XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
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/