TITLE: GCN CIRCULAR NUMBER: 13041 SUBJECT: GRB 120311B: Swift-BAT refined analysis DATE: 12/03/11 21:31:25 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), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), F. E. Marshall (NASA/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-120 to T+258 sec from recent telemetry downlinks, we report further analysis of BAT GRB 120311B (trigger #517489) (Marshall, et al., GCN Circ. 13038). The BAT ground-calculated position is RA, Dec = 258.551, -13.068 deg, which is RA(J2000) = 17h 14m 12.2s Dec(J2000) = -13d 04' 05.0" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 62%. The mask-weighted light curve shows two nearly separated peaks, the first starting at ~T-15 sec, peaking at ~T_0, and the minimum between the two peaks is at ~T+5 sec. The second peak peaks at ~T+10 sec, and returns to baseline at ~T+22 sec. T90 (15-350 keV) is 28.2 +- 5.5 sec (estimated error including systematics). The time-averaged spectrum from T-13.88 to T+21.63 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.96 +- 0.14. The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+9.04 sec in the 15-150 keV band is 1.5 +- 0.2 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/517489/BA/