TITLE:   GCN CIRCULAR
NUMBER:  29701
SUBJECT: GRB 210323B: Swift/BAT-GUANO detection and possible arcminute localization
DATE:    21/03/24 02:57:29 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 210323B (T0: 2021-03-23 12:03:33 UTC,
Fermi/GBM TRIGGER 638193818).

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 best fit duration of ~8 seconds.
With a maximum likelihood analysis (DeLaunay et al. 2021, in prep.) on
the event-mode data we detect a location for the burst with a square
root of the test statistic, sqrt(TS), of 11.77. The sqrt(TS) behaves
similarly to SNR.

This is a low significance detection and it could not be recovered
using the normal BAT imaging technique, so there is a chance that this
localization may be incorrect.

The BAT position is
RA, Dec = 259.664, +15.677 deg which is
  RA(J2000)  = 17h 18m 39.36s
  Dec(J2000) =  +15d 40' 37.20"
with an estimated uncertainty of 6 arcmin.

The partial coding was 10.6%

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/