Transformation of the Poynting flux into the kinetic energy in relativistic jets

TL;DR

This paper investigates how relativistic jets convert electromagnetic energy into kinetic energy, identifying two collimation regimes and their effects on jet acceleration and energy dominance over large distances.

Contribution

It introduces the concepts of equilibrium and non-equilibrium collimation regimes and analyzes their impact on jet acceleration and energy conversion.

Findings

Equilibrium jets reach equipartition and become matter dominated only at very large distances.

Non-equilibrium jets remain Poynting dominated over large distances.

Focused flow occurs in non-equilibrium jets accelerated to equipartition at finite distances.

Abstract

The acceleration of relativistic jets from the Poynting to the matter dominated stage is considered. The are generally two collimation regimes, which we call equilibrium and non-equilibrium, correspondingly. In the first regime, the jet is efficiently accelerated till the equipartition between the kinetic and electro-magnetic energy. We show that after the equilibrium jet ceases to be Poynting dominated, the ratio of the electro-magnetic to the kinetic energy decreases only logarithmically so that such jets become truly matter dominated only at extremely large distances. Non-equilibrium jets remain generally Poynting dominated till the logarithmically large distances. In the only case when a non-equilibrium jet is accelerated till the equipartition level, we found that the flow is not continued to the infinity but is focused towards the axis at a finite distance from the origin.