Waves in pulsar winds

TL;DR

This paper reviews wave phenomena in pulsar winds, focusing on the transition from MHD-dominated inner regions to charge-deficient outer regions, using a relativistic two-fluid model to analyze electromagnetic modes.

Contribution

It introduces a two-fluid model to analyze nonlinear electromagnetic modes in the outer pulsar wind, revealing two distinct solutions for wave propagation.

Findings

Two solutions for circularly polarized electromagnetic modes exist in the outer wind.

One solution becomes a vacuum wave, the other decelerates and is confined.

The model enhances understanding of wave behavior in charge-deficient regions.

Abstract

The radio, optical, X-ray and gamma-ray nebulae that surround many pulsars are thought to arise from synchrotron and inverse Compton emission. The energy powering this emission, as well as the magnetic fields and relativistic particles, are supplied by a "wind" driven by the central object. The inner parts of the wind can be described using the equations of MHD, but these break down in the outer parts, when the density of charge carriers drops below a critical value. This paper reviews the wave properties of the inner part (striped wind), and uses a relativistic two-fluid model (cold electrons and positrons) to re-examine the nonlinear electromagnetic modes that propagate in the outer parts. It is shown that in a radial wind, two solutions exist for circularly polarised electromagnetic modes. At large distances one of them turns into a freely expanding flow containing a vacuum wave, whereas the other decelerates, corresponding to a confined flow.