TITLE:   GCN CIRCULAR
NUMBER:  12600
SUBJECT: GRB 111129A: Swift detection of a burst with an optical counterpart
DATE:    11/11/29 16:27:24 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

J. L. Racusin (NASA/GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
S. Campana (INAF-OAB), P. A. Evans (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
C. J. Saxton (UCL-MSSL), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), M. C. Stroh (PSU), C. A. Swenson (PSU),
E. Troja (NASA/GSFC/ORAU) and B.-B. Zhang (PSU) report on behalf of
the Swift Team:

At 16:18:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111129A (trigger=508712).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 307.441, -52.724, which is 
   RA(J2000)  =  20h 29m 46s
   Dec(J2000) = -52d 43' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a few weak peaks
with a total duration of about 20 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 16:19:46.5 UT, 92.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 307.43460, -52.71300 which is
equivalent to:
   RA(J2000)  = 20h 29m 44.30s
   Dec(J2000) = -52d 42' 46.8"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 42 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 3.24
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 95 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	20:29:44.15 = 307.43395
  DEC(J2000) = -52:42:46.5  = -52.71291
with a 90%-confidence error radius of about 0.64 arc sec. This position is 1.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.06 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin AT nasa.gov). 
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.)