TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3512 SUBJECT: GRB 050603: Swift-BAT refined analysis of a long three-spiked burst DATE: 05/06/03 11:38:08 GMT FROM: David Palmer at LANL E. Fenimore (LANL), L. Angelini (GSFC-JHU)L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), J. Greiner (MPE), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), A. Retter (PSU) T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC) on behalf of the Swift/BAT team: At 06:29:05.2 UT, Swift-BAT detected GRB 050603 (trigger=131560) (GCN Circ 3509, Retter et al.). The refined BAT ground position is (RA,Dec) = 39.982,-25.195, [deg; J2000] {02:39:56; -25:11:41} (~1 arcminute statistical and systematic error radius, 95% containment). This is about 45 arcseconds from the on-board derived position. This source was near the edge of the field of view, 41 degrees from the boresight in the short direction, directly illuminating only 9% of the detector array. The mask-weighted lightcurve of the burst shows three fast-rise-exponential-decay (FRED) spikes, peaking at T-2.7, T-0.85 and T+0.15 with each spike having a width of ~0.6 s (FWHM). The third spike is ~3x the height of each of the first two spikes and produced the original image detection. Additional tail emission continues to decay after the third spike, extending to T+10. The photon index of the time-averaged spectrum is well-fit over the 15-350 keV energy band by a power law of index 1.22 +/- 0.06 with a normalization at 50 keV of (2.96 +/- 0.10) x 10^-2 photons/s/cm^2/keV. The fluence in the 15-350 keV band is 1.30 x 10^-5 erg/cm^2. The peak flux is 31.8+/1.7 photons/cm^2/s for the 1 second interval starting at T-0.18 s. Due to the current engineering mode of the spacecraft, XRT and UVOT observations will be delayed until a Target Of Opportunity pointing is manually commanded.