GCN Circular 8753

V. La Parola (INAF-IASFPA), S. D. Barthelmy (GSFC), P. J. Brown (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
J. A. Kennea (PSU), W.B Landsman (GSFC), V. Mangano (INAF-IASFPA),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
B. Sbarufatti (INAF-IASFPA) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 20:36:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081230 (trigger=338633).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 37.315, -25.142 which is 
   RA(J2000) = 02h 29m 16s
   Dec(J2000) = -25d 08' 29"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 50 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~50 sec after the trigger. 

The XRT began observing the field at 20:38:16.7 UT, 124.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 37.33148,
-25.14645 which is equivalent to:
   RA(J2000)  = 02h 29m 19.56s
   Dec(J2000) = -25d 08' 47.2"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 56 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 in excess of the Galactic value (1.68e+20
cm^-2, Kalberla et al. 2005), with an excess column of 3.2
(+2.81/-2.34) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
132 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 19.2 mag. 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
0.01. 

Burst Advocate for this burst is V. La Parola (laparola AT ifc.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.)