TITLE: GCN CIRCULAR NUMBER: 21838 SUBJECT: GRB 170906A: Swift-BAT refined analysis DATE: 17/09/06 20:53:57 GMT FROM: Scott Barthelmy at NASA/GSFC J. R. Cummings (CPI), S. D. Barthelmy (GSFC), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. H. Siegel (PSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+603 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170906A (trigger #770957) (Siegel, et al., GCN Circ. 21821). The BAT ground-calculated position is RA, Dec = 203.949, -47.088 deg, which is RA(J2000) = 13h 35m 47.7s Dec(J2000) = -47d 05' 18.3" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 67%. The mask-weighted light curve shows multiple peaks starting at ~T-40 sec, with a max peak at ~T+30, and returning to baseline at ~T+170 sec. T90 (15-350 keV) is 88.1 +- 1.5 sec (estimated error including systematics). The time-averaged spectrum from T-44.9 to T+121.5 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.21 +- 0.10, and Epeak of 205.4 +- 71.9 keV (chi squared 36.4 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.2 +- 0.0 x 10^-5 erg/cm2 and the 1-sec peak flux measured from T+29.82 sec in the 15-150 keV band is 10.9 +- 0.4 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.45 +- 0.02 (chi squared 52.7 for 57 d.o.f.). 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/770957/BA/