TITLE: GCN CIRCULAR NUMBER: 20838 SUBJECT: GRB 170307A (trigger 741528): Swift-BAT refined analysis DATE: 17/03/08 13:59:24 GMT FROM: Amy Lien at GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), N. Gehrels (GSFC), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-12 to T+963 sec from the recent telemetry downlink, we determine that BAT trigger #741528 (Lien et al., GCN Circ. 20832) is indeed a GRB, which also detected by Fermi GBM (Hui et al., GCN Circ. 20835). We report further analysis of BAT GRB 170307A (trigger #741528). The BAT ground-calculated position is RA, Dec = 13.510, 9.538 deg which is RA(J2000) = 00h 54m 02.5s Dec(J2000) = +09d 32' 17.9" with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 43%. The mask-weighted light curve shows a weak structure with several overlapping pulses that starts at ~T+55 s and ends at ~T+125 s. The burst emission might start before it came into the BAT FOV at ~T-12 s. T90 (15-350 keV) is 56.92 +- 27.40 sec (estimated error including systematics). The time-averaged spectrum from T+55.33 to T+124.69 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.88 +- 0.23. The fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+69.72 sec in the 15-150 keV band is 1.4 +- 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/741528/BA/