GCN Circular 6137

J. L. Racusin (PSU), L. M. Barbier (NASA/GSFC),
S. D. Barthelmy (GSFC), M. M. Chester (PSU),
G. Cusumano (INAF-IASFPA), D. Grupe (PSU), J. A. Kennea (PSU),
D. M. Palmer (LANL), R. L. C. Starling (U Leicester) and
L. Vetere (PSU) report on behalf of the Swift Team:

At 20:27:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070224 (trigger=261880).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 178.990, -13.340 which is 
   RA(J2000)  =  11h 55m 58s
   Dec(J2000) = -13d 20' 23"
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 25 sec.  The peak count rate
was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:30:21 UT, 143 seconds after the
BAT trigger. XRT found a bright, fading, uncatalogued X-ray source
located at RA, Dec 179.0257, -13.3294 which is
   RA(J2000)  =  11h 56m 06.2s
   Dec(J2000) = -13d 19' 46.0"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). 
This location is 131 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 3.1e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 153 seconds after the BAT trigger, and a
finding chart of nominal 400 seconds with the V filter starting 259
seconds after the BAT trigger. No 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 3-sigma upper limit in White at the XRT
position is 19.3 mag. The 8'x8' region for the list of sources
generated on-board covers 100% of the XRT error circle. No correction
has been made for the expected extinction corresponding to E(B-V) of
0.06.