TITLE: GCN CIRCULAR NUMBER: 18754 SUBJECT: GRB 151228A: Swift-BAT refined analysis DATE: 15/12/29 15:37:40 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlinks, we report further analysis of BAT GRB 151228A (trigger #668543) (Ukwatta, et al., GCN Circ. 18731). The BAT ground-calculated position is RA, Dec = 214.017, -17.665 deg, which is RA(J2000) = 14h 16m 04.0s Dec(J2000) = -17d 39' 52.7" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted light curve shows a single spike starting at ~T-0.05, peaking at ~T+0.03, and ending at ~T+0.3. T90 (15-350 keV) is 0.27 +- 0.01 sec (estimated error including systematics). The time-averaged spectrum from T-0.036 to T+0.276 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.85 +- 0.20. The fluence in the 15-150 keV band is 8.4 +- 1.1 x 10^-8 erg/cm2. The 1-sec peak photon flux measured from T-0.38 sec in the 15-150 keV band is 0.9 +- 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/668543/BA/