GRB 210306B: Swift-BAT refined analysis

Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210306B (trigger #1036024) (D'Ai, et al., GCN Circ. 29601). The BAT ground-calculated position is RA, Dec = 331.813, 10.152 deg which is RA(J2000) = 22h 07m 15.1s Dec(J2000) = +10d 09' 06.8" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 21%. The BAT light curve showed a multi-peaked structure that starts at T-2 s and ends at ~T+25 s. T90 (15-350 keV) is 24.32 +- 2.45 sec (estimated error including systematics). The time-averaged spectrum from T-2.42 to T+24.63 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.38 +- 0.20. The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+1.04 sec in the 15-150 keV band is 2.4 +- 0.5 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/1036024/BA/