GCN Circular 3296

L. Barbier (GSFC), D. Palmer (LANL), D. Burrows (PSU), A. Blustin (MSSL),
C. Markwardt (GSFC/UMd), N. Gehrels (GSFC), P. Roming (PSU)

At 04:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on-board GRB050421 (trigger # 115135).   The BAT on-board
calculated location is RA, Dec 307.241, +73.665 (20:28:58, 73:39:54) 
(J2000) with an uncertainty of 4 arcmin (radius, 3-sigma, including estimated
systematic uncertainty). The BAT light curve showed a weak, 
multipeak  structure with a duration of  about 10 seconds. The peak
count rate was measured by BAT to be 1000 counts/sec
in the 15 - 350 keV band.

The Swift spacecraft slewed promptly onto the BAT position and
observations by the Swift X-Ray Telescope (XRT) began at 04:13:42 UT
with the XRT in the auto state. An uncatalogued X-ray source was 
detected at the following position: RA, Dec 307.2542, +73.6528 
(20:29:01, 73:39:10) (J2000) with an uncertainty of 5
arcsec (radius).  This is 46 arcsec from the BAT position 
reported above.

The Swift Ultra-Violet/Optical Telescope (UVOT) began observations 112
seconds after the burst at 04:13:44 UT.  Information on UVOT 
observations will be published in the next GCN.