We investigate how the angular structure of GRB jets effects the afterglow light curves at different viewing angles , \theta _ { v } , from the jet symmetry axis .
A numerical hydrodynamical modeling for the evolution of a relativistic collimated outflow , as it interacts with the surrounding medium , is carried out , and compared to two simple models that make opposite and extreme assumptions for the degree of lateral energy transfer .
The Lorentz factor , \Gamma , and kinetic energy per unit solid angle , \epsilon , are initially taken to be power laws of the angle \theta from the jet axis .
We find that the lateral velocity in the comoving frame , v ^ { \prime } _ { \theta } , is typically much smaller than the sound speed , c _ { s } , as long as \Gamma \gg 1 , and the dynamics of relativistic structured jets may be reasonably described by a simple analytic model where \epsilon is independent of time , as long as \Gamma ( \theta = 0 ) \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } % } \hbox { $ > $ } } } a few .
We perform a qualitative comparison between the resulting light curves and afterglow observations .
This constrains the jet structure , and poses problems for a ‘ universal ’ jet model , where all GRB jets are assumed to be intrinsically identical , and differ only by our viewing angle , \theta _ { v } .