A Numerical Gamma-Ray Burst Simulation Using Three-Dimensional Relativistic Hydrodynamics: The Transition from Spherical to Jetlike Expansion

We present the first unrestricted, three-dimensional relativistic hydrodynamical calculations of the blob of gas associated with the jet that produces a gamma-ray burst. We investigate the deceleration phase of the blob, which corresponds to the time when afterglow radiation is produced, concentrating on the transition in which the relativistic beaming γ-1 goes from being less than θ, where γ is the bulk Lorentz factor and θ is the angular …