TITLE: GCN CIRCULAR NUMBER: 15163 SUBJECT: GRB 130831B, Swift-BAT refined analysis DATE: 13/09/01 21:51:29 GMT FROM: Tilan Ukwatta at MSU W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+902 sec from the recent telemetry downlink, we report further analysis of BAT GRB 130831B (trigger #568855) (Malesani, et al., GCN Circ. 15141). The BAT ground-calculated position is RA, Dec = 192.454, -29.187 deg which is RA(J2000) = 12h 49m 48.9s Dec(J2000) = -29d 11' 13.5" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 14%. BAT mask-weighted light curve shows a multi peak episode starting from ~T-12 sec highest peak around T+1 sec and ending at ~T+30 sec. T90 (15-350 keV) is 37.8 +- 10.4 sec (estimated error including systematics). The time-averaged spectrum from T-13.9 to T+30.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.88 +- 0.21. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band is 2.4 +- 0.5 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/568855/BA/