TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4217 SUBJECT: GRB 051109: Swift-BAT refined analysis DATE: 05/11/09 04:25:01 GMT FROM: Takanori Sakamoto at NASA/GSFC 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), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: Using the data set from T-60 to T+70 sec from the recent telemetry downlink, we report further analysis of BAT GRB 051109 (trigger #163136) (Tagliaferri, et al., GCN 4213). The BAT ground-calculated position is (RA,Dec) = 330.295, +40.836 {22h 01m 10.7s, +40d 50' 10.5"} [deg; J2000] +-2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 9%. The lightcurve has two peaks. The initial strong peak starts at T-5 sec with a duration of 20 sec. The second weaker peak starts at T+21 sec. with a duration of 20 sec. T90 (15-350 keV) is (36 +- 2) sec (estimated error including systematics). The power law index of the time-averaged spectrum is 1.5 +- 0.2. The fluence in the 15-150 keV band is (2.1 +- 0.3) x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T0+0.4 sec in the 15-150 keV band is (3.7 +- 0.7) ph/cm2/sec. All the quoted errors are at the 90% confidence level.