TITLE: GCN CIRCULAR NUMBER: 13949 SUBJECT: GRB 121031A, Early peak observed with Swift-BAT DATE: 12/11/03 02:06:03 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift GRB 121031A, Early peak observed with Swift-BAT J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (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): With an additional data set from T-240 to T-61 sec, we report further analysis of BAT GRB 121031 (trigger #537195) (D'Elia, et al., GCN Circ. 13934). In an earlier circular (Barthelmy, et al., GCN Circ. 13936) we described the second of two equal-sized peaks from this burst. BAT triggered on that second peak. The earlier peak occurred during a pre- planned slew maneuver, and its time interval was not covered by the data available at the time the circular was produced. The entire burst had two large peaks at T-190 and T0 that were about the same in flux, duration, and shape. Each was a FRED about 60 seconds long as seen in BAT. There was a small peak at T-50 sec of about 5 seconds duration. For the entire burst, T90 (15-350 keV) was 226 +- 19 sec (estimated error including systematics). The time-averaged spectrum from T-209.0 to T+98.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.50 +- 0.05. The fluence in the 15-150 keV band is 7.8 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T-190.72 sec in the 15-150 keV band is 2.4 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.