Constraining the Structure of Gamma‐Ray Burst Jets through the Afterglow Light Curves

We investigate the effect that the structure of GRB jets has on the afterglowlight curves for observers located at different viewing angles, $\theta_{obs}$,from the jet symmetry axis. The largest uncertainty in the jet dynamics is thedegree of lateral energy transfer. Thus, we use two simple models, that makeopposite and extreme assumptions for this point, and calculate the light curvesfor an external density that is either homogeneous, or decreases as the squareof the distance from the source. The Lorentz factor and kinetic energy per unitsolid angle are initially taken to be power laws of the angle from the jetaxis. We perform a qualitative comparison between the resulting light curvesand afterglow observations. This constrains the jet structure, and posesproblems for a `universal' jet model, where all GRB jets are assumed to beintrinsically identical, and differ only by our viewing angle, $\theta_{obs}$.Comment: 19 pages, 7 figures; submitted to ApJ in November 200