GCN Circular 42147

A. Melandri (INAF-OAR), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU),
R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII),
N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 19:43:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251007B (trigger=1402467).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 102.117, -10.303 which is 
   RA(J2000) = 06h 48m 28s
   Dec(J2000) = -10d 18' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to the continued on-board processing of the
previous burst (GRB 251007A) the BAT lightcurve is not immediately available.

The XRT began observing the field at 19:45:35.0 UT, 148.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 102.13232, -10.30328 which is
equivalent to:
   RA(J2000)  = 06h 48m 31.76s
   Dec(J2000) = -10d 18' 11.8"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 54 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 5.99
x 10^21 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 151 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Results from the list of sources
generated on-board are not available at this time. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.785.

Burst Advocate for this burst is A. Melandri (andrea.melandri AT inaf.it).
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/)