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

Abstract

We investigate the effect that the structure of gamma-ray burst (GRB) jets has on the afterglow light curves for observers located at different viewing angles, theta_obs, from the jet symmetry axis. The largest uncertainty in the jet dyanmics is the degree of lateral energy transfer. Thus, we use two simple models that make opposite and extreme assumptions for this point and calculate the light curves for an extenal density that is either homogeneous or decreases as a square of the distance from the source. The Lorentz factor, Gamma, and kinetic energy per unit solid angle, epsilon, are taken to be power laws of the angle theta from the jet axis: epsilon propto theta^-a, Gamma propto theta^-b. We perform a qualitative comparison between the resulting light curves and afterglow observations. This constrains the jet structure, and we find that a ~ 2 and 0