The Evolution of Pulsar Wind Nebulae inside Supernova Remants

Young pulsar wind nebulae (PWNe), the synchrotron nebulae powered by the rotation energy of the central neutron star, are a major source of high-energy emission in the Milky Way. Despite many decades of the study, many important questions remain concerning these objects including the particle content of the pulsar wind (is it composed solely of electrons and positrons or are there some ions in this flow), and how are particles accelerated in PWNe to the energies required to explain their observed high-energy emission. In order to properly interpret their broadband spectra to determine the answers to these questions, it is necessary to understand the evolution of PWNe as they interact with the supernova remnant (SNR) formed in the progenitor explosion. This is particularly important for PWNe which show signatures of having collided with the supernova reverse shock - believed to be the case for several PWNe detected at TeV energies by HESS. I will present a new, analytical, hydrodynamical model for the evolution of a PWN inside a SNR and show how this model can be used to constrain the properties of the central neutron star and progenitor supernova - vital information in analyzing the broadband spectrum of these sources.