Pulsar Wind Nebulae

TL;DR

Pulsar Wind Nebulae are complex, evolving structures powered by pulsars, exhibiting diverse morphologies and spectra across the electromagnetic spectrum, influenced by their environment and the properties of their central neutron stars.

Contribution

This paper provides a comprehensive overview of the characteristics, evolution, and observational features of pulsar wind nebulae across different stages.

Findings

PWNe exhibit diverse morphologies and spectral behaviors.

Evolution depends on neutron star properties and surrounding medium.

Extended gamma-ray halos form during late evolutionary stages.

Abstract

Pulsar Wind Nebulae (PWNe), structures powered by energetic pulsars, are known for their detection across the entire electromagnetic spectrum, with diverse morphologies and spectral behaviour between these bands. The temporal evolution of the morphology and spectrum of a PWN depends strongly on the properties of the associated neutron star, the relativistic outflow powered by its rotational energy, and surrounding medium, and thereby can vary markedly between objects. Due the continuous, but decreasing, injection of electrons and positrons into the PWN by the pulsar, the brightness and spectral variation within and amongst their wind nebulae reflect the magnetic field structure and particle transport within the PWN. This can include complex motions such as reverse flows or turbulence due to shock interactions and disruption to the nebula. During the last stage of the PWN's evolution, when the neutron star moves supersonically with respect to its environment, the escape of accelerated particles into the surrounding medium creates an extensive halo evident in very-high-energy gamma-rays. This chapter describes some of the identifying characteristics and key aspects of pulsar wind nebulae through their several evolutionary stages.