A Dynamical Model for the Evolution of a Pulsar Wind Nebula Inside a Nonradiative Supernova Remnant

Abstract

A pulsar wind nebula inside a supernova remnant provides a unique insight into the properties of the central neutron star, the relativistic wind powered by its loss of rotational energy, its progenitor supernova, and the surrounding environment. In this paper, we present a new semi-analytic model for the evolution of such a pulsar wind nebula. This model couples the dynamical and radiative evolution of the pulsar wind nebulae, traces the evolution of the pulsar wind nebulae throughout the lifetime of the supernova remnant produced by the progenitor explosion, and predicts both the dynamical (e.g. radius and expansion velocity) and radiative (radio to TeV γ-ray spectrum) properties of the pulsar wind nebula during this period. As a result, it is uniquely qualified for using the observed properties of a pulsar wind nebula in order to constrain the physical characteristics of the neutron star, pulsar wind, progenitor supernova, and surrounding interstellar medium. We also discuss the expected evolution for a particular set of these parameters, and show that it reproduced the large spectral break observed in radio and X-ray observations of many young pulsar wind nebulae, and the low break frequency, low radio luminosity and high TeV γ-ray luminosity, and high magnetization observed for several older pulsar wind nebulae. The predicted spectrum of this pulsar wind nebula also contains spectral features during different phases of its evolution detectable with new radio and γ-ray observing facilities such as the Extended Very Large Array and the Fermi Gamma-ray Space Telescope. Finally, this model has implications for determining if pulsar wind nebulae can inject a sufficient number of energetic electrons and positrons into the surrounding interstellar medium to explain the recent measurements of the cosmic ray positron fraction by PAMELA and the cosmic ray lepton spectrum by ATIC and HESS.

XMM-NewtonandSUZAKUdetection of an X-ray emitting shell around the pulsar wind nebula G54.1+0.3

“…We have compared the PWN and SNR sizes with the prediction of the evolutionary model of Gelfand et al (2009) for composite SNRs, and we found excellent agreement. We conclude that the faint diffuse emission around the PWN G54.1+0.3 may indeed be the shell of the associated remnant.…”

“…If the faint diffuse emission that we have discovered around the PWN G54.1+0.3 is really the associated SNR shell, then we can compare its properties with the PWN-SNR evolutionary model of Gelfand et al (2009). This model couples the dynamical and radiative evolution of the PWN with the dynamical properties of the surrounding non-radiative SNR, and predicts several distinctive evolutionary stages, namely the initial expansion, the reverse shock collision, the re-expansion, and the second compression.…”

“…This is somewhat disconcerting for the consolidated picture of a remnant of a core-collapse supernova, which indicates that the PWN is expanding inside the host supernova remnant, producing a variety of complex phenomena, such as reverberation, Rayleigh-Taylor instability at the interface between the PWN and ejecta, and rejuvenation of the shell (e.g., van der Swaluw et al 2001;Blondin et al 2001;Chevalier 2005;Gelfand et al 2009, and references therein). One reason may be the lack of deep observations targeting the PWN surroundings.…”

Pulsar-Wind Nebulae

“…This naturally explains the observed high degree of polarization in X-rays, optical, and radio (Moran et al 2013;Bietenholz et al 2004;Weisskopf et al 1978). Multiwavelength observations and modeling show that IC scattering on Cosmic Microwave Background and NIR/IR background starts to dominate PWN spectra in GeV (Acero et al 2013) and completely dominates synchrotron at TeV energies (Atoyan and Aharonian 1996, Volpi et al 2008, Gelfand et al 2009, and Olmi et al 2014; see the Crab and Vela PWN spectra in Fig. 14 for example).…”

Fermi-LAT constraints on the pulsar wind nebula nature of HESS J1857+026

“…The significant offset of the pulsar from the γ-ray centroid implies either a PWN expansion into an inhomogenous medium, or an asymmetric reverse shock interaction. Either way, models such as Gelfand et al (2009) which compute the PWN compression assuming spherical symmetry cannot be applied.…”