GRB 221226B Swift-BAT refined analysis

Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 221226B (trigger #1145959) (Cenko, et al., GCN Circ. 33108). The BAT ground-calculated position is RA, Dec = 22.903, -41.515 deg which is RA(J2000) = 01h 31m 36.7s Dec(J2000) = -41d 30' 52.5" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 97%. The mask-weighted light curve shows a pulse of approximately 4 seconds total duration and some substructure. T90 (15-350 keV) is 3.44 +- 0.57 sec (estimated error including systematics). The time-averaged spectrum from T+0.22 to T+4.28 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.16 +- 0.13. The fluence in the 15-150 keV band is 5.4 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.24 sec in the 15-150 keV band is 2.6 +- 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/1145959/BA/