TITLE: GCN CIRCULAR NUMBER: 29611 SUBJECT: GRB 210305A: Swift-BAT refined analysis DATE: 21/03/07 13:13:21 GMT FROM: Takanori Sakamoto at AGU H. A. Krimm (NSF), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), A. D'Ai (INAF-IASFPA), S. Laha (GSFC/UMBC), 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+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210305A (trigger #1035922) (D'Ai, et al., GCN Circ. 29595). The BAT ground-calculated position is RA, Dec = 319.808, 34.548 deg which is RA(J2000) = 21h 19m 13.9s Dec(J2000) = +34d 32' 52.8" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 74%. The BAT light curve showed a complex structure with a duration of about ~100 sec. T90 (15-350 keV) is 68.6 +- 4.4 sec (estimated error including systematics). The time-averaged spectrum from T-21.65 to T+71.76 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.93 +- 0.19, and Epeak of 104.1 +- 19.7 keV (chi squared 43.93 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 7.1 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+0.26 sec in the 15-150 keV band is 3.4 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.49 +- 0.04 (chi squared 71.71 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/1035922/BA/