TITLE: GCN CIRCULAR NUMBER: 20220 SUBJECT: GRB 161129A: Swift-BAT refined analysis DATE: 16/11/30 02:02:40 GMT FROM: Amy Lien at GSFC S. D. Barthelmy (GSFC), J. R. Cummings (CPI), N. Gehrels (GSFC), H. A. Krimm (NSF/USRA), D. Kocevski (NASA/MSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. P. Norris (BSU), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 161129A (trigger #724438) (Kocevski, et al., GCN Circ. 20210). The BAT ground-calculated position is RA, Dec = 316.221, 32.137 deg which is RA(J2000) = 21h 04m 53.1s Dec(J2000) = +32d 08' 11.9" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 69%. The mask-weighted light curve shows a short spike from ~T0 to ~T+0.2 s, followed by several overlapping pulses that last until ~T+45 s. T90 (15-350 keV) is 35.53 +- 2.09 sec (estimated error including systematics). The time-averaged spectrum from T+0.06 to T+44.58 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.57 +- 0.06. The fluence in the 15-150 keV band is 3.6 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+26.64 sec in the 15-150 keV band is 3.4 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Because the light curve seems to resemble that of a short GRB with extended emission (Norris et al. 2010), we perform further analysis of the short spike. Using a 4-ms binned light curve, the lag analysis finds a lag of 4 +/- 3 ms for the 50-100 keV to 15-25 keV band, which is consistent with that of a short GRB. However, the spectral fit of the short spike using a simple power-law model gives a power-law index of 1.9 +/- 0.3. This value is on the softer end of short GRBs, and also softer than all the initial pulses of those short GRBs with extended emission (Lien et al. 2016). The power-law index of the spectrum for the rest of the light curve is 1.53 +/- 0.06, which is harder than the initial spike and thus unexpected from a short GRB with extended emission. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/724438/BA/