Hydrodynamic Collimation of Relativistic Outflows: Semianalytic Solutions and Application to Gamma-Ray Bursts

TL;DR

This paper presents semianalytic models for the collimation of relativistic outflows, specifically applied to gamma-ray bursts, analyzing how surrounding media influence jet structure and opening angles.

Contribution

It introduces new semianalytic solutions for the structure of baryon-poor jets confined by static corona or disk winds, with implications for GRB emission.

Findings

Jet opening angle depends on confining medium parameters.

Shock structure can converge or diverge, affecting jet collimation.

Inner flow may have a non-uniform ultra-relativistic core.

Abstract

A model is developed for the confinement and collimation of a baryon poor outflow by its surrounding medium. Both, confinement by kinetic pressure of a static corona, and confinement by the ram pressure of a supersonic wind emanating from a disk surrounding the inner source are considered. Solutions are presented for the structure of the shocked layers of a deflected baryon poor jet (BPJ) and exterior wind. The dependence of the opening angle of the BPJ on the parameters of the confining medium are carefully examined. It is found that the BPJ shock may either converge to the symmetry axis or diverge away from it, depending on the opening angle of the BPJ injection cone. In the latter case the inner flow exhibits a non-uniform structure, consisting of an ultra-relativistic core containing the unshocked BPJ enveloped by the slower, shocked BPJ layer. The implications of our results to the prompt GRB emission are briefly discussed.