Pulsar Wind Nebulae as a Source of Cosmic-Ray Electrons and Positrons

Abstract

Cosmic-ray electron positron (e ^±) observations by PAMELA, H.E.S.S, Fermi and AMS-02 have reported possible excesses of the fluxes with respect to the standard theoretical prediction in an energy range of from a few 10–100 GeV. Pulsar wind nebulae (PWNe) are a promising source of the excesses; multi-wavelength observations of PWNe have shown that e ^±s are accelerated up to PeV energies in situ and the inferred acceleration rate can be sufficient to provide the observed e ^± flux. An uncertain point of this scenario is whether, how and when the accelerated e ^±s can escape PWNe, which is also the key question for understanding the PWN physics.

In this chapter, we first review the classical model of cosmic-ray e ^±s and the observational history. Possible origins of the e ^± excess are generally discussed. Then, focusing on the PWN model, we consider the minimum requirements to be an e ^± source and the observational signatures. We show that O(100) of pulsars with age of < 10⁷ yrs and within a few kpc from the Earth or the nearby Geminga and Mongem pulsars alone can explain the observed e ^± excess. On the other hand, the young nearby Vela pulsar can contribute to e ^± cosmic rays with multiple-TeV energies. We discuss future prospects for testing the PWN scenarios and e ^± escape from the PWNe with using CALET, DAMPE, and CTA.