TITLE: GCN CIRCULAR NUMBER: 11202 SUBJECT: GRB 100902A: Swift-BAT refined analysis DATE: 10/09/04 01:15:41 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from telemetry downlinks, we report further analysis of BAT GRB 100902A (trigger #433160) (Sakamoto, et al., GCN Circ. 11181). The BAT ground-calculated position is RA, Dec = 48.626, 30.970 deg, which is RA(J2000) = 03h 14m 30.3s Dec(J2000) = +30d 58' 13.2" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 72%. The mask-weighted light curve shows several strong peaks. The first starts around T-60 sec and returns to background around T+70 sec. We note that this burst location came into the BAT FoV around T-80 sec, so there could have been prior activity for this burst. Then come two stronger peaks at ~T+130 and ~T+205 sec; then a smaller peak at ~T+400 sec. T90 (15-350 keV) is 428.8 +- 43.0 sec (estimated error including systematics). The time-averaged spectrum from T-49.5 to T+409.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.98 +- 0.13. The fluence in the 15-150 keV band is 3.2 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+207.89 sec in the 15-150 keV band is 1.0 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/433160/BA/