Three-Dimensional Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. II. Relaxation of Pulsar Wind Nebula

TL;DR

This study uses 3D relativistic MHD simulations to analyze how the current-driven kink instability relaxes pulsar wind nebulae, showing that magnetic energy decreases significantly and axisymmetric models overestimate elongation.

Contribution

It demonstrates that 3D simulations reveal lower magnetization levels and less elongation than axisymmetric models, challenging previous assumptions about pulsar wind nebulae structure.

Findings

Magnetization parameter  declines from 0.3 to 0.01.

Axisymmetric models overestimate nebula elongation.

Magnetic energy flux remains a significant fraction after dissipation.

Abstract

We have investigated the relaxation of a hydrostatic hot plasma column containing toroidal magnetic field by the Current-Driven (CD) kink instability as a model of pulsar wind nebulae. In our simulations the CD kink instability is excited by a small initial velocity perturbation and develops turbulent structure inside the hot plasma column. We demonstrate that, as envisioned by Begelman, the hoop stress declines and the initial gas pressure excess near the axis decreases. The magnetization parameter \sigma, the ratio of the Poynting to the kinetic energy flux, declines from an initial value of 0.3 to about 0.01 when the CD kink instability saturates. Our simulations demonstrate that axisymmetric models strongly overestimate the elongation of the pulsar wind nebulae. Therefore, the previous requirement for an extremely low pulsar wind magnetization can be abandoned. The observed structure of the pulsar wind nebulae do not contradict the natural assumption that the magnetic energy flux still remains a good fraction of the total energy flux after dissipation of alternating fields.