TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3364 SUBJECT: GRB050505 Swift-BAT refined analysis DATE: 05/05/06 02:12:32 GMT FROM: Hans Krimm at NASA-GSFC D. Hullinger (UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), L. Cominsky (Sonoma State), J. Cummings (GSFC/NRC), E. Fenimore (LANL), R. Fink (GSFC), M. Galassi (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), M. Tashiro (Saitama U.), J. Tueller (GSFC), on behalf of the Swift/BAT team: At 23:22:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB050505 (trigger=117504) (GCN Circ 3360, Hurkett et al.). The refined BAT ground position is (RA,Dec) = 141.787, +30.245, [deg; J2000] +- 3 arcmin, (95% containment). The burst was 49 degrees off the Swift boresight, which is ~30% coded. The BAT mask-weighted light curve shows a multi-peaked structure with a total duration T90 (15-350 keV) 60 +- 2 seconds (estimated error including systematics). The initial peak began ~15 seconds before the trigger and extended to 10 seconds after the trigger. There were three further short peaks beginning at T+20 seconds, T+31 seconds, and T+49 seconds. The spectrum is well fit by a simple power law with photon index of 1.5 +- 0.1. The fluence in the 15-350 keV band is (4.1 +- 0.4) x 10^-6 erg/cm2. The 1-second peak photon flux in the 15-350 band is (2.2 +- 0.3) ph/cm2/s recorded at 1 second after the trigger. All the quoted errors are at the 90% confidence level. We note that this burst appears to be well-suited for ground follow-up observations, as it is located 90 degrees from the Sun, 120 degrees from the Moon, close to the ecliptic, and away from the Galactic plane.