GCN Circular 22082

T. N. Ukwatta (LANL), D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA),
V. D'Elia (ASDC), Alex Deich (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 15:20:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171102B (trigger=785510).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 288.103, +22.438 which is 
   RA(J2000) = 19h 12m 25s
   Dec(J2000) = +22d 26' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 15:22:33.3 UT, 123.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 288.07776, 22.44512 which is equivalent
to:
   RA(J2000)  = 19h 12m 18.66s
   Dec(J2000) = +22d 26' 42.4"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 87 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 http://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 4.51
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
124 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image covers none of the
XRT error circle. 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 18.0 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.75. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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/too.html.)