Propagation and stability of superluminal waves in pulsar winds

TL;DR

This paper investigates superluminal electromagnetic waves in pulsar winds, analyzing their propagation, stability, and potential role as precursors to termination shocks, with implications for different pulsar environments.

Contribution

It introduces an integrable system for superluminal wave evolution in spherical pulsar winds and assesses their stability across various astrophysical conditions.

Findings

Confined superluminal modes can form stable precursors to termination shocks.

Stability of these modes depends on external pressure, being stable in most isolated pulsars.

Modes may become unstable in high-pressure environments like starburst galaxy nebulae.

Abstract

Nonlinear electromagnetic waves with superluminal phase velocity can propagate in the winds around isolated pulsars, and around some pulsars in binary systems. Using a short-wavelength approximation, we find and analyze an integrable system of equations that govern their evolution in spherical geometry. A confined mode is identified that stagnates to finite pressure at large radius and can form a precursor to the termination shock. Using a simplified criterion, we find this mode is stable for most isolated pulsars, but may be unstable if the external pressure is high, such as in the pulsar wind nebulae in starburst galaxies and in W44. Pulsar winds in eccentric binary systems, such as PSR 1259-63, may go through phases with stable and unstable electromagnetic precursors, as well as phases in which the density is too high for these modes to propagate.