TITLE: GCN CIRCULAR NUMBER: 21832 SUBJECT: GRB 170906C: Swift-BAT refined analysis DATE: 17/09/06 14:56:29 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), 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-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170906C (trigger #770981) (Siegel, et al., GCN Circ. 21826). The BAT ground-calculated position is RA, Dec = 128.659, 70.805 deg, which is RA(J2000) = 08h 34m 38.1s Dec(J2000) = +70d 48' 16.7" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 32%. The mask-weighted light curve shows multiple overlapping peaks starting at ~T-40 sec, peaking at ~T+7 sec, and returning to baseline at ~T+100 sec. T90 (15-350 keV) is 48.4 +- 4.7 sec (estimated error including systematics). The time-averaged spectrum from T-35.21 to T+39.22 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.30 +- 0.22, and Epeak of 104.8 +- 43.0 keV (chi squared 47.9 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 8.8 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+6.18 sec in the 15-150 keV band is 7.2 +- 0.5 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.67 +- 0.05 (chi squared 56.9 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/770981/BA/