TITLE: GCN CIRCULAR NUMBER: 23166 SUBJECT: GRB 180821A: Swift-BAT refined analysis DATE: 18/08/22 13:15:43 GMT FROM: Hans Krimm at NSF/NASA-GSFC H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), A. Tohuvavohu (PSU), 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 downlink, we report further analysis of BAT GRB 180821A (trigger #854578) (Tohuvavohu, et al., GCN Circ. 23158). The BAT ground-calculated position is RA, Dec = 7.739, -38.612 deg which is RA(J2000) = 00h 30m 57.4s Dec(J2000) = -38d 36' 41.9" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%. The mask-weighted light curve showed a broad peak with some structure, running from ~T+0 to T+70 sec. T90 (15-350 keV) is 64.00 +- 22.6 sec (estimated error including systematics). The time-averaged spectrum from T+1.00 to T+65.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.79 +- 0.31. The fluence in the 15-150 keV band is 1.4 +- 0.3 x 10^-6 erg/cm2. Since the peak was so broad, the automated analysis software was unable to derive a significant peak photon flux at the highest point in the light curve, T+56.5 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/854578/BA/