TITLE: GCN CIRCULAR NUMBER: 18256 SUBJECT: GRB 150907B: Swift-BAT refined analysis DATE: 15/09/08 12:27:43 GMT FROM: Scott Barthelmy at NASA/GSFC H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. G. R. Roegiers (PSU), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlinks, we report further analysis of BAT GRB 150907B (trigger #654803) (Roegiers, et al., GCN Circ. 18249). The BAT ground-calculated position is RA, Dec = 255.265, -63.798 deg, which is RA(J2000) = 17h 01m 03.5s Dec(J2000) = -63d 47' 51.6" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 50%. The mask-weighted light curve shows a Fred-like starting at ~T-1 sec, peaking at ~T+1 sec, and ending around T+100 sec. T90 (15-350 keV) is 62.0 +- 11.1 sec (estimated error including systematics). The time-averaged spectrum from T-1.48 to T+64.53 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.17 +- 1.03, and Epeak of 67.4 +- 29.7 keV (chi squared 53.2 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+0.59 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.47 +- 0.18 (chi squared 59.8 for 57 d.o.f.). 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/654803/BA/