TITLE: GCN CIRCULAR NUMBER: 21384 SUBJECT: GRB 170728B, Swift-BAT refined analysis DATE: 17/07/29 19:04:42 GMT FROM: Amy Lien at GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), J. R. Cummings (CPI), 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 170728B (trigger #765130) (Cenko et al., GCN Circ. 21371). The BAT ground-calculated position is RA, Dec = 238.019, 70.111 deg which is RA(J2000) = 15h 52m 04.5s Dec(J2000) = +70d 06' 40.0" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 5%. The mask-weighted light curve shows a short multi-peaked structure from ~T-0.1 s to ~T+0.7 s, followed by some weak emission till ~T+50 s, Fermi/GBM also reports emission till ~T+47 s (Stanbro et al., GCN Circ. 21383). T90 (15-350 keV) is 47.7 +- 25.2 sec (estimated error including systematics). The time-averaged spectrum for the short pulse from T-0.1 to T+0.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index -1.10 +- 1.71, and Epeak of 82.0 +- 24.2 keV (chi squared 51.71 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 6.2 +- 1.1 x 10^-7 erg/cm2. A fit to a simple power law gives a photon index of 1.21 +- 0.24 (chi squared 61.25 for 57 d.o.f.). The time-averaged spectrum for the extended emission from T+0.7 to T+50.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.25 +- 0.57. The fluence in the 15-150 keV band is 9.8 +- 3.9 x 10^-7 erg/cm2. 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/765130/BA/