GCN Circular 18678

P. A. Evans (U Leicester), S. D. Barthelmy (GSFC), J. A. Kennea (PSU),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 03:12:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 151210A (trigger=666931).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 65.182, -71.230 which is 
   RA(J2000)  =  04h 20m 44s
   Dec(J2000) = -71d 13' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple of peaks
with a duration of about 60 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~14 sec after the trigger. 

The XRT began observing the field at 03:15:26.7 UT, 150.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 65.1177,
-71.2509 which is equivalent to:
   RA(J2000)  = 04h 20m 28.25s
   Dec(J2000) = -71d 15' 03.4"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 105 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.30
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 150 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 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.12. 

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