GCN Circular 41262

N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB),
J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU),
K. L. Page (U Leicester) and C. Salvaggio (INAF-OAB) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 10:46:08.44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250807A (trigger=1340514). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA, Dec 51.420, -47.877 which is 
   RA(J2000) = 03h 25m 41s
   Dec(J2000) = -47d 52' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex structure 
with a duration of about 80 sec.  The peak count rate
was ~19000 counts/sec (15-350 keV), at ~35 sec after the trigger.

The XRT began observing the field at 10:47:49.5 UT, 101.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 51.4478, -47.8880 which is equivalent to:
   RA(J2000)  = 03h 25m 47.47s
   Dec(J2000) = -47d 53' 16.8"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 77 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 111 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	03:25:47.59 =  51.44829
  DEC(J2000) = -47:53:16.2  = -47.88782
with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.98 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.011.

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu).
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/)