Cosmological X‐Ray Flashes in the Off‐Axis Jet Model

The <V/V_{max}> of the cosmological X-ray flashes detected by Wide Field Cameras on BeppoSAX is calculted theoretically in a simple jet model. The total emission energy from the jet is assumed to be constant. We find that if the jet opening half-angle is smaller than 0.03 radian, the theoretical <V/V_{max}> is less than $\\sim0.4$, which is consistent with the recently reported observational value of $0.27\\pm 0.16$ in 1 $\\sigma$ level. This suggests that the off-axis GRB jet with the small opening half-angle at the cosmological distance can be identified as the cosmological X-ray flash.

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