Ioka and Nakamura (2001) proposed a simple jet model that is compatible with<br />
the peak luminosity-spectral lag relation, the peak luminosity-variability<br />
relation and various other relations in the Gamma-Ray Bursts. If the viewing<br />
angle is much larger than the collimation angle of the jet in the model by Ioka<br />
and Nakamura, for appropriate model parameters we obtain the observational<br />
characteristics of the X-ray flashes, such as the peak flux ratio and the<br />
fluence ratio between the $\gamma$-ray (50-300 keV) and the X-ray band (2-10<br />
keV), the X-ray photon index, the typical duration and the eve...