TITLE:   GCN CIRCULAR
NUMBER:  41581
SUBJECT: GRB 250828B: Swift detection of a burst
DATE:    25/08/28 22:56:15 GMT
FROM:    David Palmer at LANL <palmer@lanl.gov>

P. A. Evans (U Leicester), R. Gupta (NASA GSFC), J. A. Kennea (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 22:33:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250828B (trigger=1345836).  Swift could not slew to the
burst due to an observing constraint.
The BAT on-board calculated location is 
RA, Dec 124.852, -17.388 which is 
   RA(J2000) = 08h 19m 24s
   Dec(J2000) = -17d 23' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 8 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger.

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 17:55 UT on 2025 September 07. There will thus be no XRT
or UVOT data for this trigger before this time.

We note that this GRB is coincident within one minute with a 
subthreshold Gravitational Wave trigger S250828ef, at 
22:32:44 UT. However, this GW trigger is of low confidence, rated
as 99% likely to be Terrestrial background noise.

Burst Advocate for this burst is P. A. Evans (pae9 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/)