NASA Swift Detection of GRB050509b: A short duration burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 3381
SUBJECT: Swift Detection of GRB050509b: A short duration burst
DATE: 05/05/09 05:03:23 GMT
FROM: Louis M Barbier at NASA/GSFC/Swift lmb@cosmicra.gsfc.nasa.gov

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), S. Holland (GSFC/USRA) on behalf of the Swift Team;

At 04:00:19.23 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050509b (trigger #118749). The BAT on-board calculated location is RA, dec 189.056, +29.000 (12h 36m 13s, +29d 00′ 01”) (J2000) with an uncertainty of 4 arcmin (radius, 3-sigma, including estimated systematic uncertainty). The BAT light curve showed a single short spike with a duration of less than 128 milliseconds. The peak count rate measured by BAT was about 2100 counts/sec in the 15 – 350 keV band.

The Swift spacecraft slewed promptly onto the BAT position. The XRT imaged the field at 04:01:12 (53.0 s 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 Telescope (UVOT) observations began at 04:01:09.8 UT, 50 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 100 sec after the BAT trigger. Based on a preliminary comparison with the DSS, there is a possible low significance source at RA=12:36:18, DEC=29:01:24 which is not present in the DSS. It has a V-band magnitude of 18.8.