GCN Circular 42039

A. P. Beardmore (U Leicester), J. A. Kennea (PSU), M. J. Moss (GSFC)
and K. L. Page (U Leicester) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 14:17:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251001B (trigger=1400467).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 42.665, -23.020 which is 
   RA(J2000) = 02h 50m 40s
   Dec(J2000) = -23d 01' 09"
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 25 sec.  The peak count rate
was ~2,000 counts/sec (15-350 keV), at ~4 sec after the trigger.

The XRT began observing the field at 14:19:17.0 UT, 116.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 42.65098, -23.02014
which is equivalent to:
   RA(J2000)  = 02h 50m 36.24s
   Dec(J2000) = -23d 01' 12.5"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 46 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.65
x 10^20 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 860 seconds after the BAT trigger. No credible afterglow
candidate has been found in the initial data products. Data from the 2.7'x2.7'
sub-image are not available at this time. The 8'x8' region for the list of
sources generated on-board covers 100% of the XRT error circle. The list of
sources is typically complete to about 18 mag. No correction has been made for
the expected extinction corresponding to E(B-V) of 0.023.

Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.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/)