Gamma-ray burst afterglows from jetted shocks in wind environments

Abstract

Gamma-ray bursts with long durations are widely thought to arise from the collapse of massive stars, where the wind environment is unavoidable. It is also believed that $γ$-ray bursts come from jets. Considering these two points in this paper, we calculate the evolution of a highly collimated jet that expands in a stellar wind environment and the expected afterglow from such a jet. We use a set of refined dynamical equations and a realistic lateral speed of the jet, and find: (1) There is no observable break at the time when the Lorentz factor of the jet is equal to the inverse of its initial half-opening angle. (2) No obvious break appears at the time when the blast wave transits from the relativistic to the non-relativistic phase. (3) For the wind case, there is no flattening tendency even up to $10^9$ s. (4) Compared with the homogeneous medium case, our calculated flux is weaker in the stellar wind case. Finally, we find that two kinds of GRB models (neutron star mergers and massive star collapses) may be discriminated in our numerical results.