The Evolution and Structure of Pulsar Wind Nebulae

Abstract

Pulsars steadily dissipate their rotational energy via relativistic winds.Confinement of these outflows generates luminous pulsar wind nebulae, seen across the electromagnetic spectrum in synchrotron and inverse Compton emission, and in optical emission lines when they shock the surrounding medium. These sources act as important probes of relativistic shocks, particle acceleration and of interstellar gas. We review the many recent advances in the study of pulsar wind nebulae, with particular focus on the evolutionary stages through which these objects progress as they expand into their surroundings, and on morphological structures within these nebulae which directly trace the physical processes of particle acceleration and outflow. We conclude by considering some exciting new probes of pulsar wind nebulae, including the study of TeV gamma-ray emission from these sources, and observations of pulsar winds in close binary systems.

A new study of the supernova remnant G344.7-0.1 located in the vicinity of the unidentified TeV source HESS J1702-420

“…For a PWN a flat radio spectrum with α between ∼-0.3 and 0 is expected (Gaensler & Slane 2006). The spectrum obtained is in principle compatible with the PWN predicted values.…”

New expansion rate measurements of the Crab nebula in radio and optical

“…For a spherical pulsar wind nebula expanding into un-shocked supernova ejecta, both theory and simulations predict an approximately power-law expansion, with m in the range of 1.1 to 1.3 (e.g. Chevalier 1984;van der Swaluw et al 2001;Bucciantini et al 2003;Gaensler & Slane 2006). Our results are therefore consistent with the theoretical expectations, albeit at the higher end of the range of expected values of m.…”

Diffuse γ-ray emission in the vicinity of young star cluster Westerlund 2

“…Formally, this could be be sufficient to explain the detected γ-ray luminosity by high energy photons produced in the surrounding pulsar nebulae. However the huge extension of the detected diffuse radiation (200 pc) significantly exceeds the typical size of PWNe (see, e.g., Gaensler & Slane 2006). Thus a single PWN originating the whole diffuse γ-ray emission seems also unlikely.…”