GCN Circular 29947

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

Swift/BAT did not trigger on GRB 210506A (T0: 2021-05-06 00:39:48.54
UTC, INTEGRAL/SPI-ACS trigger 9191).

The INTEGRAL/SPI-ACS 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 90 seconds of BAT event-mode data from
[-45,+45] seconds around the time of the burst. All the requested
event mode data was delivered to the ground.

The burst is strongly detected in BAT with a duration of ~0.2 seconds.

The position of the burst was found with the typical BAT imaging
procedure with an SNR of 6.8.
We note that this position would imply an extremely hard spectrum for
this burst, beyond what is typically expected. This could imply that
the position is incorrect, or that this is a truly exceptional event.
We encourage other GRB instruments to provide spectral measurements
that can help clarify the situation.

The BAT position is
RA, Dec = 132.853, 4.582 deg which is
   RA(J2000)  = 08h 51m 24.72s
   Dec(J2000) =  04d 34��� 55.2���
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/