TITLE: GCN CIRCULAR NUMBER: 10072 SUBJECT: GRB 091024: Swift-BAT refined analysis DATE: 09/10/24 17:40:10 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+483 sec from the recent telemetry downlink, we report further analysis of BAT GRB 091024 (trigger #373674) (Mashall, et al., GCN Circ. 10062). The BAT ground-calculated position is RA, Dec = 339.240, 56.885 deg, which is RA(J2000) = 22h 36m 57.6s Dec(J2000) = +56d 53' 07.8" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 39%. The mask-weighted light curve shows two slightly overlapping FRED peaks. The first starts at ~T-20 sec, peaks at ~T+2 sec. The second peaks at ~T+42 sec and long-term low-level emission extends out to ~T+400 sec. T90 (15-350 keV) is 109.8 +- 16.7 sec (estimated error including systematics). The time-averaged spectrum from T-15.2 to T+135.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.20 +- 0.08. The fluence in the 15-150 keV band is 6.1 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T-0.23 sec in the 15-150 keV band is 2.0 +- 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/373674/BA/