TITLE: GCN CIRCULAR NUMBER: 10265 SUBJECT: GRB 091208B, Swift-BAT refined analysis DATE: 09/12/08 15:59:30 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), C. Pagani (PSU), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 091208B (trigger #378559) (Pagani, et al., GCN Circ. 10256). The BAT ground- calculated position is RA, Dec = 29.411, 16.881 deg which is RA(J2000) = 01h 57m 38.5s Dec(J2000) = +16d 52' 50.7" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 10%. The mask-weighted light curve shows two separated FRED peaks. The first at T0 was weaker and softer than the second at T+8 sec. T90 (15-350 keV) is 14.9 +- 3.7 sec (estimated error including systematics). The time-averaged spectrum from T-0.2 to T+22.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.74 +- 0.11. The fluence in the 15-150 keV band was 3.3 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+8.1 sec in the 15-150 keV band was 15.2 +- 1.0 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/378559/BA/