GCN Circular 5017

S. Campana (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC),
C. B. Markwardt (GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-OAB) and D. E. Vanden Berk (PSU)
report on behalf of the Swift Team:

At 08:54:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060428B (trigger=207399).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA,Dec 235.350,+62.010
{15h 41m 24s,+62d 00' 36"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty).  This is
an image trigger (128 sec), so the lightcurve does not show any significant
activity (as is typical). 

The XRT began observing the field at 08:58:02 UT, 204 seconds after the
BAT trigger. XRT found a bright, fading X-ray source
located at RA(J2000) = 15h 41m 25.6s, Dec(J2000) = +62d 01' 25.6", with an
estimated uncertainty of 5.0 arcseconds (90% confidence radius). 
This location is 51 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
2.3e-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 212 seconds after the BAT trigger,
and of 400 sec. with the V filter starting at 965 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 V band 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 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  0.01.