TITLE: GCN CIRCULAR NUMBER: 21973 SUBJECT: GRB 171004A: Swift-BAT refined analysis DATE: 17/10/04 21:13:14 GMT FROM: Amy Lien at GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU) (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 171004A (trigger #776347) (Cenko et al., GCN Circ. 21966). The BAT ground-calculated position is RA, Dec = 139.150, 52.684 deg which is RA(J2000) = 09h 16m 35.9s Dec(J2000) = +52d 41' 01.5" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curve shows several overlapping peaks that starts at ~ T+9 and ends at ~ T+160 s. The burst location went out of the BAT FOV at ~ T+580 s, and thus we only have information of the burst emission before then. T90 (15-350 keV) is 107.1 +- 14.5 sec (estimated error including systematics). The time-averaged spectrum from T+9.08 to T+138.31 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.67 +- 0.12. The fluence in the 15-150 keV band is 3.0 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+48.34 sec in the 15-150 keV band is 0.9 +- 0.3 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/776347/BA/