GCN Circular 13993

B. N. Barlow (PSU), S. D. Barthelmy (GSFC), D. Grupe (PSU),
E. A. Helder (PSU) and C. J. Mountford (U Leicester) report on behalf
of the Swift Team:

At 08:32:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121125A (trigger=539563).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 228.520, +55.322 which is 
   RA(J2000) = 15h 14m 05s
   Dec(J2000) = +55d 19' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 70 sec.  The peak count rate
was ~4600 counts/sec (15-350 keV), at ~34 sec after the trigger. 

The XRT began observing the field at 08:33:34.1 UT, 66.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 228.52496, 55.31330 which
is equivalent to:
   RA(J2000)  = 15h 14m 05.99s
   Dec(J2000) = +55d 18' 47.9"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 32 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 in excess of the Galactic value (1.27 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.7
(+2.20/-1.89) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.27e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	15:14:06.54 = 228.52724
  DEC(J2000) = +55:18:48.0  =  55.31332
with a 90%-confidence error radius of about 0.74 arc sec. This position is 1.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.19 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is B. N. Barlow (bnb2 AT psu.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/too.html.)