TITLE: GCN CIRCULAR NUMBER: 6811 SUBJECT: GRB 070920B, Swift-BAT refined analysis DATE: 07/09/21 13:22:10 GMT FROM: Scott Barthelmy at NASA/GSFC S.D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), J.L. Racusin (PSU), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070920B (trigger #291728) (Racusin, et al., GCN Circ. 6808). The BAT ground-calculated position is RA, Dec = 0.127, -34.844 deg which is RA(J2000) = 00h 0m 30.5s Dec(J2000) = -34d 50' 39" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted lightcurve shows a symmetrical peak starting at ~T-20 sec, peaking at ~T+1 sec, and ending at ~T+17 sec. T90 (15-350 keV) is 20.2 +- 0.2 sec (estimated error including systematics). The time-averaged spectrum from T-11.2 to T+13.4 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.67 +- 0.58, and Epeak of 41.3 +- 4.5 keV (chi squared 45.21 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 6.6 +- 0.5 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T-0.49 sec in the 15-150 keV band is 0.8 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.00 +- 0.10 (chi squared 67.16 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. [GCN OPS NOTE(21sep07): Per author's request, the 'B' was added to the GRB name in the first sentence.]