TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4393
SUBJECT: GRB051221A: Suzaku WAM observation of the prompt emission
DATE:    05/12/24 05:10:53 GMT
FROM:    Kazutaka Yamaoka at Aoyama Gakuin U  <yamaoka@phys.aoyama.ac.jp>

Y.Endo, M.Tashiro, K.Abe, S. Hong, K.Onda (Saitama U.), 
K.Yamaoka, S.Sugita (Aoyama Gakuin U.), M.Ohno, 
T.Takahashi, Y.Fukazawa (Hiroshima U.), Y.Terada (RIKEN), 
K.Nakazawa, G.Sato, T.Takahashi (ISAS/JAXA), R.Miyawaki, 
M.Kokubun, K.Makishima (Univ. of Tokyo) and the HXD-II team

The bright and short burst, GRB 051221A (Parsons et al., GCN4363),
triggered by Swift/BAT was also detected with the Suzaku Wideband
All-sky Monitor (WAM) which covers an energy band of 50 keV - 5 MeV
at 01:51:16 (UT).
The observed light curve exhibits two intense short spikes
with a total duration (T90) of 0.22 sec. 
The fluence in 100 - 2000 keV was (2.4 +/- 0.4)X10^-6 erg/cm2. 
The 1-sec peak flux was 4.7 +/- 0.8 photons/cm2/s in the 
same energy range.

Preliminary result shows that the time-averaged spectrum 
is well fitted by a single power law with a photon index 
of 1.95 +/- 0.18. 

All the quoted errors are at statistical 90% confidence level.
The WAM onboard calibration is still under way, and 
systematic errors, such as the flux calibration uncertainties of
about 20%, are not included in the errors.

The WAM light curve of this event is available at 
http://www.astro.isas.ac.jp/suzaku/research/HXD-WAM/WAM-GRB/grb/grb_table.html

Further detailed analyses are in progress.