TITLE: GCN CIRCULAR NUMBER: 8428 SUBJECT: GRB 081028, Swift-BAT refined analysis DATE: 08/10/28 11:54:31 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (INAF-OAB), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), 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+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 081028 (trigger #332851) (Guidorzi, et al., GCN Circ. 8421). The BAT ground-calculated position is RA, Dec = 121.893, 2.305 deg, which is RA(J2000) = 08h 07m 34.4s Dec(J2000) = +02d 18' 16.8" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 85%. The mask-weighted light curve shows two main peaks and a tail. The first peak starts at ~T+20 sec, peaks at ~T+80 sec, and falls to a minumum betwen the two peaks at ~T+140 sec. The second peak peaks at ~T+220 sec. There is a tail out to approximately T+400 sec. T90 (15-350 keV) is 260 +- 40 sec (estimated error including systematics). The time-averaged spectrum from T+29.3 to T+441.5 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.25 +- 0.38, and Epeak of 58 +- 23 keV (chi squared 57.6 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.7 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+211.74 sec in the 15-150 keV band is 0.5 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.84 +- 0.09 (chi squared 63.9 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/332851/BA/