TITLE:   GCN CIRCULAR
NUMBER:  45676
SUBJECT: GRB 260921A: Swift detection of a burst
DATE:    26/09/21 09:52:28 GMT
FROM:    K.L. Page at U Leicester <klp5@leicester.ac.uk>

K. L. Page (U Leicester), V. D'Elia (SSDC & INAF-OAR),
S. Dichiara (PSU), R. A. J. Eyles-Ferris (U Leicester),
N. P. M. Kuin (UCL-MSSL), D. M. Palmer (LANL), T. M. Parsotan (GSFC)
and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 09:29:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 260921A (trigger=1512356).  Swift did not automatically slew
to the burst. The BAT on-board calculated location is
RA, Dec (145.373, +2.852), which is
   RA(J2000) = 9h 41m 29s
   Dec(J2000) = +2d 51' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The available BAT light curve (cut off at
T+8 s) showed a complex structure with a duration of about 10 sec.
The peak count rate was ~4500 counts/sec (15-350 keV), at ~1 sec
after the trigger.

Swift's automatic slews are currently disabled, and the burst is Sun
constrained until 8th October, so there will be no XRT or UVOT data for
this trigger.

This is the first BAT-triggered GRB since GRB 260127A.  Since then,
Swift has been hibernating in preparation for the LINK reboost attempt.
With the rescope of that mission, Swift has been returned to
operation and we will continue to make science observations for
as long as possible until re-entry.

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)