The spectral properties of the GRB prompt gamma-ray emission observed by the Suzaku Wide-band All-sky Monitor.

We report on the observational results of GRBs by the Suzaku Wide-band All-sky Monitor (WAM) in these two years since the Suzaku launch. Using the WAM data, we can investigate the spectral properties of the prompt emission of GRBs with a wider energy band and the highest sensitivity than any previous GRB missions. We found that the spectral properties between short and long GRBs, such as the spectral parameter distribution, the hardness ratio, the spectral lag, and the total emitting energy are clearly different even in the MeV energy band. This result implies that different progenitors or different bulk Lorentz factors of the ejecta are likely causes for the difference between these two classes. We also found that there is a strong correlation between the peak energy and the isotropic equivalent luminosity of the time-resolved spectra of the bright long GRB 061007, and found that this correlation can be separated well between rising and decay phase of each pulse. This indicates that the physical condition changes during the pulse phase of the burst. [ABSTRACT FROM AUTHOR]
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