T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
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 191221B (trigger #945521)
(Laha et al., GCN Circ. 26534). The BAT ground-calculated position is
RA, Dec = 154.831, -38.152 deg which is
RA(J2000) = 10h 19m 19.3s
Dec(J2000) = -38d 09' 07.1"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 12%.
The mask weighted light curve shows complex structures with a duration of ~30 s.
The overall structure starts at ~T-10 s and lasts till ~T+20s.
There is some hint of weak emission extending up to ~ T+60 s.
T90 (15-350 keV) is 48.00 +- 16.00 sec (estimated error including systematics).
The time-averaged spectrum from T-15.28 to T+96.72 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.24 +- 0.05. The fluence in the 15-150 keV band is 1.9 +- 0.1 x 10^-05 erg/cm2.
the fluence of this burst is among the brightest ~3% of all BAT-detected GRBs
(based on fluences from the BAT GRB catalog https://swift.gsfc.nasa.gov/results/batgrbcat/).
The 1-sec peak photon flux measured from T+8.22 sec in the 15-150 keV band
is 4.8 +- 0.7 ph/cm2/sec. All the quoted errors are at the 90% confidence
The results of the batgrbproduct analysis are available at