TITLE:   GCN CIRCULAR
NUMBER:  28971
SUBJECT: GRB 201128B: Swift/BAT-GUANO detection and arcminute localization
DATE:    20/11/30 23:46:57 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie Kennea (PSU) report:

Swift/BAT did not trigger on GRB 201128B (T0: 2020-11-28 17:54:11 UTC,
Fermi/GBM TRIGGER 628278856).

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 ~15 seconds. This was
a weak and slow burst that occurred during a rapid part of a Swift
slew. The position of the burst was found with a novel and
uncalibrated slew image mosaicing procedure, and so the positional
uncertainty is not yet well characterized.


The BAT position is
RA, Dec = 339.354, -49.246 deg which is
   RA(J2000)  = 22h 37m 24.96s
   Dec(J2000) =  -49d 14’ 45.6”
with an estimated uncertainty of at least 5 arcmin.

This position is consistent with the Fermi GBM localization
(https://gcn.gsfc.nasa.gov/other/628278856.fermi).

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/