A unified model of short and long gamma-ray bursts, X-ray-rich gamma-ray bursts, and X-ray flashes

Taking into account the recent suggestion that a short gamma-ray burst (GRB) looks like the first 1 s of a long GRB, we propose that the jet of a GRB consists of multiple subjets or subshells (i.e., an inhomogeneous jet model). The multiplicity of the subjets along a line of sight n(s) is an important parameter. If n(s) is large (much greater than1) the event looks like a long GRB, while if n(s) is small (similar to1) the event looks like a short GRB. If our line of sight is off-axis to any subjets, the event looks like an X-ray flash or an X-ray-rich GRB. The lognormal distribution of durations of short and long GRBs are also suggested in the same model.