TITLE: GCN CIRCULAR NUMBER: 13733 SUBJECT: GRB 120909A: Swift-BAT refined analysis DATE: 12/09/09 15:03:07 GMT FROM: Scott Barthelmy at NASA/GSFC T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), S. Immler (CRESST/GSFC/UMD), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC) (i.e. the Swift-BAT team): Using the data set from T-41 to T+556 sec from recent telemetry downlinks, we report further analysis of BAT GRB 120909A (trigger #533060) (Immler, et al., GCN Circ. 13727). The BAT ground-calculated position is RA, Dec = 275.735, -59.432 deg which is RA(J2000) = 18h 22m 56.5s Dec(J2000) = -59d 25' 55.2" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows multiple overlapping peaks. The burst was already occurring when Swift-BAT came out of the SAA at ~T-40 sec. The observed peaks occurred at ~T-38, ~T+1, ~T+28, and ~T+48 sec. The burst returned to baseline at ~T+200 sec. There is a possible peak at ~T+490 to ~T+580 sec, at which point Swift had to slew due to an observing constraint and the location went out of the BAT FoV. The time-averaged spectrum from T-38.98 to T+95.17 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.39 +- 0.06. The fluence in the 15-150 keV band is 6.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.88 sec in the 15-150 keV band is 1.8 +- 0.3 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/533060/BA/