GCN Circular 4848

L. Angelini (GSFC), S. Barthelmy (GSFC), D. Burrows (PSU),
M. Chester (PSU), J. Cummings (GSFC/ORAU), N. Gehrels (GSFC),
M. Goad (U Leicester), H. Krimm (GSFC/USRA), F. Marshall (GSFC),
D. Palmer (LANL)
on behalf of the Swift team:

At 00:49:10 UT, Swift-BAT triggered and located GRB 060306 (trigger=200638).
The spacecraft slewed immediately.  The BAT on-board calculated location is
RA,Dec 41.099d,-2.153d {02h 44m 24s,-02d 09' 10"} (J2000), with an uncertainty
of 3 arcmin (radius, 90% containment, stat+sys).  The BAT light curve shows
a multi-peak structure with a total duration of 30 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~1 seconds after the trigger.

The XRT began observing the field at 00:50:38 UT (88 sec after the trigger).
The XRT found a bright, fading, uncataloged X-ray source at 
RA(J2000)  = 2h 44m 22.7s
Dec(J2000) = -2d 8' 54"
with an estimated uncertainty of 5.4" (90% radius).  This position is
24 arcseconds from the BAT position.  The initial flux is 1.2E-9 ergs/cm2/sec.

UVOT took a finding chart exposure of 200 seconds with the V filter starting
93 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 18.4 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 of about 0.1 magnitudes.

We are currently in the Malindi downlink gap, and so we will not receive
the complete data set for another 6 hours.