GCN Circular 3379

C. Hurkett, E. Rol, (U Leicester), L. Barbier (GSFC), S. Barthelmy (GSFC),
A. Blustin (MSSL), D. Burrows (PSU),  J. Cummings (GSFC/NRC),
N. Gehrels (GSFC),  J. Kennea (PSU), C. Markwardt (GSFC/UMD), on behalf of
the Swift Team;

At 01:46:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB050509 (trigger=118707).  The BAT on-board calculated
location is RA, Dec 310.588, +54.070 (J2000) with an uncertainty of 3
arcmin (radius, 3-sigma, including estimated systematic uncertainty).
The BAT light curve shows a single main peak with a small peak on the
rising edge (at T-6sec).  The total duration is ~13 sec. The BAT peak
count rate is ~2300 events/sec at T_zero (15-350 keV).

The Swift spacecraft slewed promptly onto the BAT position.  The XRT
imaged the field at 01:47:22.76 (54.8s after the burst), but did not find
any bright source in the field.  An XRT position will be determined by
analysis of the full data following the next ground station pass.

The Swift Ultra Violet/Optical (UVOT) observations began at
01:47:20.5 UT, 52 seconds after the BAT trigger.  The first
data taken after the spacecraft settled was a 90 sec exposure
using the V filter with the midpoint of the observation at
97 sec after the BAT trigger. Based on a preliminary comparison with the
DSS and USNO-B, we detect no new source within the BAT error
circle down to an approximate five sigma limiting magnitude of 17.3.

The observation was truncated by an observing constraint at 01:50:00 UT
after approximately 110 sec.