TITLE: GCN CIRCULAR NUMBER: 19840 SUBJECT: GRB 160821A: Swift-BAT refined analysis DATE: 16/08/22 14:04:04 GMT FROM: Amy Lien at GSFC C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. H. Siegel (PSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (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 160821A (trigger #709351) (Siegel, et al. GCN Circ. 19830). The BAT ground-calculated position is RA, Dec = 171.254, 42.345 deg which is RA(J2000) = 11h 25m 00.9s Dec(J2000) = +42d 20' 43.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 79%. The mask-weighted light curve shows a complex structure with many overlapping pulses that starts at ~T-3 s and extends beyond T+117s, when the the burst went out of the BAT FOV due to a pre-planned slew. The burst flux was rising during the slew, so it is possible that the BAT detector missed the peak emission. The main peak that is visible in the BAT light curve occurs at ~T+114 s. The time-averaged spectrum from T-2.61 to T+115.17 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.52 +- 0.06. The fluence in the 15-150 keV band is 7.2 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+113.51 sec in the 15-150 keV band is 2.8 +- 0.6 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/709351/BA/