  We have performed a joint analysis of prompt emission from four bright short
gamma-ray bursts (GRBs) with the Suzaku-WAM and the Konus-Wind experiments.
This joint analysis allows us to investigate the spectral properties of
short-duration bursts over a wider energy band with a higher accuracy. We find
that these bursts have a high E$_{\rm peak}$, around 1 MeV and have a harder
power-law component than that of long GRBs. However, we can not determine
whether these spectra follow the cut-off power-law model or the Band model. We
also investigated the spectral lag, hardness ratio, inferred isotropic
radiation energy and existence of a soft emission hump, in order to classify
them into short or long GRBs using several criteria, in addition to the burst
duration. We find that all criteria, except for the existence of the soft hump,
support the fact that our four GRB samples are correctly classified as
belonging to the short class. In addition, our broad-band analysis revealed
that there is no evidence of GRBs with a very large hardness ratio, as seen in
the BATSE short GRB sample, and that the spectral lag of our four short GRBs is
consistent with zero, even in the MeV energy band, unlike long GRBs. Although
our short GRB samples are still limited, these results suggest that the
spectral hardness of short GRBs might not differ significantly from that of
long GRBs, and also that the spectral lag at high energies could be a strong
criterion for burst classification.
