TITLE: GCN CIRCULAR NUMBER: 20855 SUBJECT: GRB 170311A: Swift-BAT refined analysis DATE: 17/03/12 16:08:13 GMT FROM: Amy Lien at GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), N. Gehrels (GSFC), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170311A (trigger #741965) (Cummings, et al. GCN Circ. 20846). The BAT ground-calculated position is RA, Dec = 280.539, -30.041 deg which is RA(J2000) = 18h 42m 09.4s Dec(J2000) = -30d 02' 27.1" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 64%. The mask-weighted light curve shows a complex structure with several overlapping peaks that starts at ~T-1 s and ends at ~T+6 s. T90 (15-350 keV) is 6.32 +- 0.96 sec (estimated error including systematics). The time-averaged spectrum from T-0.92 to T+6.08 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.38 +- 0.32. The fluence in the 15-150 keV band is 2.5 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+1.73 sec in the 15-150 keV band is 0.8 +- 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/741965/BA/