GCN Circular 5014

V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC),
S. T. Holland (GSFC/USRA), J. A. Kennea (PSU),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and D. E. Vanden Berk (PSU) report on behalf of
the Swift Team:

At 03:22:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060428 (trigger=207364).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA,Dec 123.568, -37.165
{08h 14m 16s, -37d 09' 52"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty).  The BAT light
curve shows a main peak starting at ~T-5 sec and ending at ~T+15 sec. 
There is a possible second peak going from T+20 to T+40 sec.  The peak count
rate was ~2500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 03:23:56 UT, 69 seconds after the
BAT trigger. XRT found a fading, uncatalogued X-ray source located at
RA(J2000) = 08h 14m 10.9s, Dec(J2000) = -37d 10' 09.1", with an
estimated uncertainty of 4.7 arcseconds (90% confidence radius). This
location is 65 arcseconds from the BAT on-board position, within the
BAT error circle. The initial flux in the 2.5s image was 
3.2e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 400 seconds with the V filter
starting 71 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
is about 19.1 mag. The 8'x8' region for the list of sources
generated on-board covers 100% of the XRT error circle. The limiting
magnitude is expected to be about 17.5. No correction has been made
for the large, but uncertain extinction expected.