TITLE: GCN CIRCULAR NUMBER: 5831 SUBJECT: GRB 061121, Swift-BAT refined analysis DATE: 06/11/21 21:37:11 GMT FROM: Takanori Sakamoto at NASA/GSFC E. Fenimore (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. L. Page (U Leicester), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-240 to T+421 sec from the recent telemetry downlink, we report further analysis of BAT GRB 061121 (trigger #239899) (Page, et al., GCN Circ. 5823). The BAT ground-calculated position is RA,Dec = 147.228, -13.188 deg {9h 48m 54.8s, -13d 11' 16.6"} (J2000) +- 0.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted lightcurve starts with small smooth pulse at ~T-5 sec and returning to instrumental background level at T+20 sec. The the second and much brighter started at ~T+50 sec with a series of overlapping peaks the last of which was the brightest. Then there was roughly exponential decay out to ~T+200 sec. T90 (15-350 keV) is 81 +- 5 sec (estimated error including systematics). The time-averaged spectrum from T-0.8 to T+121.8 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.41 +- 0.03. The fluence in the 15-150 keV band is 1.37 +- 0.02 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from T+74.48 sec in the 15-150 keV band is 21.1 +- 0.5 ph/cm2/sec. The isotropic equivalent energy using the reported redshift of 1.314 (GCN Circ. 5826; Bloom, Perley & Chen) is 7e52 erg in the 35 keV - 347 keV band at the GRB rest frame. All the quoted errors are at the 90% confidence level.