The structure of steady, relativistic, magnetised jets with rotation

TL;DR

This paper develops and analyzes equilibrium models of steady, relativistic, magnetized, rotating jets, exploring how magnetic fields and rotation laws influence jet structure, and tests the models with numerical simulations for potential use in further dynamical studies.

Contribution

It introduces a framework for constructing equilibrium models of relativistic jets with rotation and magnetic fields, identifying forbidden regions and validating models with numerical simulations.

Findings

Forbidden regions in magnetic pitch angle/magnetization plane identified.

Maximum magnetic field components constrained by equilibrium conditions.

Numerical simulations confirm the stability of the analytical models.

Abstract

We present equilibrium models of relativistic magnetised, infinite, axisymmetric jets with rotation propagating through an homogeneous, unmagnetised ambient medium at rest. The jet models are characterised by six functions defining the radial profiles of density, pressure, and the toroidal and axial components of velocity and magnetic field. Fixing the ambient pressure and the jet rest-mass density and axial components of the flow velocity and magnetic field, we analyze the influence of the toroidal magnetic field and several rotation laws on the structure of the equilibrium models. Our approach excludes by construction the analysis of the self-consistently magnetically launched jet models or the force-free equilibrium solutions. Several forbidden regions in the magnetic pitch angle/magnetization plane are found where models of the class considered in our study could not be settled. These forbidden regions are associated with the existence of maximum axial and toroidal magnetic field components compatible with the prescribed equilibrium condition at the jet surface, and/or an excess of centrifugal force producing gaps with negative pressures in the jet. The present study can be easily extended to jet models with different transversal profiles and magnetic field configurations. In the last part of the paper, we test the ability of our RMHD code to maintain steady equilibrium models of axisymmetric RMHD jets in one and two spatial dimensions. The one dimensional numerical simulations serve also as a consistency proof of the fidelity of the analytical steady solutions discussed in the first part of the paper. The present study allows us to build initial equilibrium jet models with selected properties for dynamical (and emission) simulations of magnetised relativistic jets with rotation.