[vsnet-grb-info 28199] GRB 210622A: Swift/BAT-GUANO detection and arcminute localization of a long burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30302
SUBJECT: GRB 210622A: Swift/BAT-GUANO detection and arcminute localization of a long burst
DATE:    21/06/22 13:59:39 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu at gmail.com>

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

Swift/BAT did not trigger on GRB 210622A (T0: 2021-06-22 01:32:35.9
UTC, Fermi/GBM GCN 30297).

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 at least 25 seconds.
We note this is different from the prompt GBM classification as ‘likely short’.
The burst morphology consists of a first bright, short, hard, peak
followed by longer emission with weaker flares.

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 18.8. The sqrt(TS) behaves
similarly to SNR.
Using the normal BAT imaging technique, we find the same location for
the GRB with an SNR of 8.1.

The BAT position is
RA, Dec = 233.117, -26.213 deg which is
   RA(J2000)  = 15h 32m 28.10s
   Dec(J2000) =  -26d 12′ 47.5″
with an estimated uncertainty of 2.5 arcmin.

This position is consistent with the Ferm/GBM localization (GCN 30297).

XRT and UVOT follow-up has been requested. Prompt followup by Swift is
delayed due to visibility constraints. 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/