TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4052 SUBJECT: GRB 051001: Swift-BAT refined analysis DATE: 05/10/02 00:18:19 GMT FROM: Hans Krimm at NASA-GSFC T. Sakamoto (GSFC/NRC), L. Angelini (GSFC-JHU), L. Barbier (GSFC), S. Barthelmy (GSFC), M. Chester (PSU), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: Using the data set from T-300 to T+300 sec from the recent telemetry downlink, we report further analysis of Swift-BAT GRB 051001 (trigger #157870) (Moretti, et al., GCN 4051). The refined BAT ground position is (RA,Dec) = 350.990,-31.523 {23h 23m 57.7s, -31d 31' 23.6"} [deg; J2000] +-2.3 arcmin, (radius, sys+stat, 90% containment). This is 1.8 arcmin from the XRT flight centroid and 0.9 arcmin from the BAT position derived onboard. The partial coding was 74 %. The mask-weighted light curve shows very broad emission starting at ~10 sec before the trigger and extending to T+195 sec. There are two main peaks: from T-10 to T+60 sec, and a stronger one from T+80 to T+180 and weak peaks ~T+185 to T+195 and T+230 to T+240 sec. There is no significant emission in the BAT energy range after T+240 out to T+1400 sec. With such a low level light curve it is difficult to estimate the duration, but our best estimate of T90 (15-350 keV) is 190 +- 10 sec (estimated error including systematics). The power law index of the time-averaged spectrum is 2.10 +- 0.15. The fluence in the 15-150 keV band is (1.8 +- 0.15) x 10^6 erg/cm2. The 1-sec peak photon flux measured from T0+153.3 sec in the 15-150 keV band is (0.51 +- 0.12) ph/cm2/sec. All the quoted errors are at the 90% confidence level.