NASA Swift Detection of the Burst GRB050509

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 3379
SUBJECT: Swift Detection of the Burst GRB050509
DATE: 05/05/09 02:47:54 GMT
FROM: Cheryl Pauline Hurkett at Leicester U

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.