TITLE: GCN CIRCULAR NUMBER: 8539 SUBJECT: GRB 081121: Swift-BAT refined analysis DATE: 08/11/22 00:09:10 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), S. R. Oates (UCL-MSSL), D. M. Palmer (LANL), 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-119 to T+271 sec from the recent telemetry downlink, we report further analysis of BAT GRB 081121 (trigger #335105) (Oates, et al., GCN Circ. 8537). The BAT ground-calculated position is RA, Dec = 89.282, -60.612 deg, which is RA(J2000) = 05h 57m 07.7s Dec(J2000) = -60d 36' 42.1" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 5%. The mask-weighted light curve shows an approximately square-shaped pulse with a trailing spike. The pulse starts at ~T-10 sec and ends at ~T=15 sec. There is a hint of low-level precursor emission starting before T-119 sec (the beginning of the saved event-by-event data). T90 (15-350 keV) is 14 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T-2.8 to T+12.9 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.43 +- 0.54, and Epeak of 123 +- 69 keV (chi squared 44.9 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 4.1 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+6.94 sec in the 15-150 keV band is 4.4 +- 1.0 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.21 +- 0.12 (chi squared 52.0 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/335105/BA/