TITLE:   GCN CIRCULAR
NUMBER:  8571
SUBJECT: GRB 081128: Swift detection of a burst
DATE:    08/11/28 17:31:30 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

R. Margutti (Univ Bicocca&OAB), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), P. J. Brown (PSU),
D. N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (ASDC),
P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester),
C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), W.B Landsman (GSFC), V. Mangano (INAF-IASFPA),
J. Mao (INAF-OAB), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester) and T. N. Ukwatta (GSFC/GWU) report
on behalf of the Swift Team:

At 17:18:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081128 (trigger=335895).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 20.798, +38.115, which is 
   RA(J2000)  =  01h 23m 12s
   Dec(J2000) = +38d 06' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The TDRSS lightcurve for this image trigger
does shows a possible peak (or possibly background variation
during the slew). 

The XRT began observing the field at 17:22:02.2 UT, 197.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 20.80537, 38.12728 which
is equivalent to:
   RA(J2000)  = 01h 23m 13.29s
   Dec(J2000) = +38d 07' 38.2"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 48 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
6.09e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 8.04e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 206 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 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
No correction has been made for the expected extinction corresponding to
E(B-V) of 0.05. 

Burst Advocate for this burst is R. Margutti (raffaella.margutti AT brera.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/too.html.)