[vsnet-grb-info 2545] GRB 051221B: Refined analysis of the Swift-BAT burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4382
SUBJECT: GRB 051221B:  Refined analysis of the Swift-BAT burst
DATE:    05/12/22 05:46:05 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), T. Takahashi (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the full data set from the recent telemetry downlink
covering T-300 to T+300 sec, we report further analysis
of Swift-BAT GRB 051221B (trigger #173904) (Boyd, et al., GCN 4376).
The ground-analysis position is RA,Dec 312.359,+53.040
{20h 49m 26.1s,+53d 02' 23.4"} (J2000)
with an uncertainty of 1.6 arcmin (radius, 90%, stat+sys).
The partial coding fraction is 45%.  The lightcurve has two,
possibly 3, peaks starting at T+49 sec with a total duration of 70 sec.
T90 is 61 +- 1 sec.  Fitting a simple power law over the full interval
from T+49 to T+119 sec, the photon index is 1.48 +/- 0.18 with a fluence
of 1.13 +/- 0.13 X 10^-6 erg/cm^2.  The peak flux in a 1-sec wide window
starting at T+59 sec is 0.54 +/- 0.20 ph/cm^2/sec.  All values are
in the 15-150 keV band at the 90% confidence level.  A final note:
we think it is very likely that this is a GRB, but we can not rule out 
the possibility that it is a hard x-ray transient.