GCN Circular 6224

C. B. Markwardt (GSFC/UMD), M. M. Chester (PSU),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
F. E. Marshall (NASA/GSFC), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU) and E. Troja (INAF-IASFPA) report on behalf
of the Swift Team:

At 03:53:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070328 (trigger=272773).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 65.117, -34.069 which is 
   RA(J2000) = 04h 20m 28s
   Dec(J2000) = -34d 04' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 70 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 03:55:21 UT, 88 seconds after the
BAT trigger. XRT found a bright, fading X-ray source located at
RA, Dec 65.1160, -34.0646 which is
   RA(J2000)  =  04h 20m 27.8s
   Dec(J2000) = -34d 03' 52.5"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). 
This location is 16 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 2.6e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 98 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 typical 3-sigma upper limit has been about 18.5 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 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.04.