Evolved Pulsar Wind Nebulae

TL;DR

This paper reviews the properties and evolution of pulsar wind nebulae, emphasizing recent discoveries of extended TeV halos and X-ray tails that reveal particle escape processes in aged systems.

Contribution

It provides a comprehensive overview of evolved pulsar wind nebulae, highlighting new observational features and insights into particle escape mechanisms in these systems.

Findings

Detection of extended TeV halos indicates efficient particle escape.

Misaligned X-ray tails reveal pulsar motion and particle outflows.

Evolved nebulae show reduced luminosity and altered morphology.

Abstract

Based on the expected population of core collapse supernova remnants and the huge number of detected pulsars in the Galaxy, still representing only a fraction of the real population, pulsar wind nebulae are likely to constitute one of the largest classes of {extended} Galactic sources in many energy bands. For simple evolutionary reasons, the majority of the population is made of evolved systems, whose detection and identification are complicated by their reduced luminosity, the possible lack of X-ray emission (that fades progressively away with the age of the pulsar), and by their modified morphology with respect to young systems. Nevertheless they have gained renewed attention in recent years, following the detection of misaligned X-ray tails protruding from an increasing number of nebulae created by fast moving pulsars, and of extended TeV halos surrounding aged systems. Both these features are clear signs of an efficient escape of particles, with energy close to the maximum acceleration limit of the pulsar. Here we discuss the properties of those evolved systems and what we have understood about the process of particle escape, and the formation of observed features.