GCN Circular 3330

A. Falcone, D. N. Burrows, M. Chester (PSU), P. Schady (MSSL),
J. Cummings (GSFC/NRC), D. Palmer (LANL), C. Pagani (PSU), B. Zhang (UNLV), 
K. Page, M. Goad (U.Leicester), N. Gehrels (GSFC)

on behalf of the Swift Team.

At 09:25:40 UT, the Swift Burst Alert Telescope (BAT) triggered
and located GRB050502b (trigger=116116).   The BAT on-board
calculated location is RA, Dec = 142.543, +17.002
(09:30:10, +17:00:07) (J2000) with an uncertainty of
3 arcmin (radius, 3-sigma, including estimated
systematic uncertainty).  The BAT light curve showed a 7-second
long peak with complex structure from t-4 to t+3.  The
maximum count rate was 4000 counts per second (15-350 keV)
in the 1 second time interval centered around t+1.

The spacecraft slewed promptly and the XRT began observations
at 09:26:43 UT.  The initial centroiding image detected only
5 counts, insufficient to produce a centroid.  Further analysis
will require the ground-processed data, which will be available
at the Swift MOC at about 12:30 UT.

The Swift Ultra Violet/Optical (UVOT) observations began at
09:26:40 UT, 60 seconds after the BAT trigger. The first
data taken after the spacecraft settled was a 100 sec
exposure using the V filter with the midpoint of the
observation at 135 sec after the BAT trigger. This image
was sent directly to the ground via TDRSS with the FOV pixel
binning set at 8 x 8 to reduce telemetry. A comparison against
the USNO-B1 reveals a new source inside the BAT error circle
at RA, Dec 09:30:12.58, +17:02:00.7 (J2000). This is 118 arcseconds from 
the BAT position.  The V-band magnitude was 17.7 +/- 0.1.