TITLE:   GCN CIRCULAR
NUMBER:  30732
SUBJECT: GRB 210827A: Swift/BAT-GUANO detection and arcminute localization
DATE:    21/08/27 21:41:58 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

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

Swift/BAT did not trigger on GRB 210827A (T0: 2021-08-27 09:59:24.34
UTC, Fermi/GBM trigger #  651751169, GCN 30724).

The Fermi/GBM 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 burst is detected in BAT with a duration of approximately 10 seconds.
Using the normal BAT imaging technique, we find the location for
the GRB with an SNR of 8.3.

The BAT position is
RA, Dec = 174.9181 +55.7858 deg which is
   RA(J2000)  = 11h 39m 40.34s
   Dec(J2000) =  +55d 47′ 08.88″
with an estimated uncertainty of 4 arcmin.

This position is consistent with the Fermi/GBM localization.

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/