Illustration of a collimated GRB outflow with an opening angle, θ_j is shown. In the case of a top-hat jet model, both the jet energy, E, and Lorentz factor, Γ, are angle independent (i.e., constant, shown in brown long dashed line) within the θ_j. On the other hand, in case of a structured jet model, the E or Γ remains a constant within the jet core, θ_c and beyond that possess a certain profile until θ_j (shown by the blue short dashed line). θ_v is the viewing angle as measured from the jet axis.