TITLE: GCN CIRCULAR NUMBER: 8708 SUBJECT: GRB 081221, Swift-BAT refined analysis DATE: 08/12/22 19:27:08 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), E. A. Hoversten (PSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+873 sec from the recent telemetry downlink, we report further analysis of BAT GRB 081221 (trigger #337889) (Hoversten, et al., GCN Circ. 8687). The BAT ground-calculated position is RA, Dec = 15.801, -24.542 deg which is RA(J2000) = 01h 03m 12.2s Dec(J2000) = -24d 32' 32.8" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 61%. The mask-weighted light curve shows two main overlapping peaks, the smaller from about T+0 to T+12 sec and the larger from about T+12 to T+40 sec, with multiple subsidiary peaks and an extended tail visible to about T+150 sec. T90 (15-350 keV) is 34 +- 1 sec (estimated error including systematics). The time-averaged spectrum from T-0.3 to T+112.6 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.21 +- 0.13, and Epeak of 69.9 +- 3.9 keV (chi squared 37.73 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.81 +- 0.03 x 10-05 erg/cm2 and the 1-sec peak flux measured from T+21.42 sec in the 15-150 keV band is 18.2 +- 0.5 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.86 (chi squared 119.90 for 57 d.o.f.). 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/337889/BA/