Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X

TL;DR

This study models the contribution of the Vela-X pulsar wind nebula to the high-energy electron and positron excess observed by AMS-02, showing Vela-X can account for the excess above 100 GeV.

Contribution

It provides a detailed propagation model linking gamma-ray observations of Vela-X to local cosmic ray electron and positron fluxes, highlighting Vela-X as a significant source.

Findings

Vela-X can explain the electron and positron excess above 100 GeV.

The excess is consistent with gamma-ray emission models of Vela-X.

Additional young pulsars may contribute at higher energies.

Abstract

We investigate, in terms of production from pulsars and their nebulae, the cosmic ray positron and electron fluxes above $\sim10$ GeV, observed by the AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from the gamma-ray photon spectrum of the source, generated via synchrotron and inverse Compton processes, we estimated the electron and positron injection spectra. Several features are fixed from observations of Vela-X and unknown parameters are borrowed from the Crab nebula. The particle spectra produced in the pulsar wind nebula are then propagated up to the Solar System, using a diffusion model. Differently from previous works, the omnidirectional intensity excess for electrons and positrons is obtained as a difference between the AMS-02 data and the corresponding local interstellar spectrum. An equal amount of electron and positron excess is observed and we interpreted this excess (above $\sim$100 GeV in the AMS-02 data) as a supply coming from Vela-X. The particle contribution is consistent with models predicting the gamma-ray emission at the source. The input of a few more young pulsars is also allowed, while below $\sim$100 GeV more aged pulsars could be the main contributors.