TITLE: GCN CIRCULAR NUMBER: 22229 SUBJECT: GRB 171209A: Swift-BAT refined analysis DATE: 17/12/10 17:50:20 GMT FROM: Amy Lien at GSFC J. R. Cummings (CPI), S. D. Barthelmy (GSFC), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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+400 sec from the recent telemetry downlink, we report further analysis of BAT GRB 171209A (trigger #796100) (LaPorte et al., GCN Circ. 22213). The BAT ground-calculated position is RA, Dec = 139.387, -30.523 deg which is RA(J2000) = 09h 17m 32.8s Dec(J2000) = -30d 31' 22.4" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 61%. The mask-weighted light curve shows a multi-peaked structure that starts at ~ T-70 s and ends at ~ T+230 s. T90 (15-350 keV) is 161.7 +- 30.8 sec (estimated error including systematics). The time-averaged spectrum from T-70.76 to T+228.44 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.58 +- 0.07. The fluence in the 15-150 keV band is 7.5 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+79.52 sec in the 15-150 keV band is 1.6 +- 0.2 ph/cm2/sec. 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/796100/BA/