Superluminal waves in pulsar winds

TL;DR

This paper investigates superluminal electromagnetic waves in pulsar winds, analyzing their properties and potential role in energy dissipation beyond the critical radius where they dominate.

Contribution

It provides a detailed analysis of the nonlinear dispersion relation of superluminal waves in pulsar winds and explores their significance in energy dissipation processes.

Findings

Superluminal waves exist beyond the critical radius in pulsar winds.

The critical radius depends on flow parameters like magnetization and luminosity.

Superluminal modes may facilitate electromagnetic energy dissipation at the termination shock.

Abstract

The energy lost by a rotation-powered pulsar is carried by a relativistic flow containing a mixture of electromagnetic fields and particles. In the inner regions, this is thought to be a magnetically dominated, cold, electron-positron wind that is well described by the MHD equations. However, beyond a critical radius r_{cr}, the same particle, energy and momentum fluxes can be transported by a strong, transverse electromagnetic wave with superluminal phase speed. We analyze the nonlinear dispersion relation of these waves for linear and circular polarization, and find the dependence of r_{cr} on the mass-loading, magnetization and luminosity of the flow, as well as on the net magnetic flux. We show that, for most isolated pulsars, the wind lies well outside r_{cr}, and speculate that superluminal modes play an important role in the dissipation of electromagnetic energy into nonthermal particles at the termination shock.