On the contribution of the bow shock pulsar wind nebula PSR J0437-4715 to the observed fluxes of GeV-TeV positrons and antiprotons

TL;DR

This paper models how the nearby pulsar PSR J0437-4715's bow shock nebula could explain the observed excesses of GeV-TeV positrons and antiprotons in cosmic rays, matching observed flux ratios.

Contribution

It provides Monte Carlo simulations and an analytical diffusion model showing PSR J0437-4715 can account for the cosmic ray positron and antiproton fluxes and ratios.

Findings

PSR J0437-4715's nebula can produce the observed positron flux from 30 GeV to 1 TeV.

The pulsar's contribution explains the energy-independent positron-to-antiproton ratio.

Approximately 25% of the pulsar's wind power suffices to match observed fluxes.

Abstract

The orbital observatories PAMELA and AMS-02 have detected a significant excess in the cosmic ray (CR) positron flux at energies above several tens of GeV. The measured values exceed those expected in models of secondary origin of positrons due to inelastic collisions of CR nuclei with the interstellar matter. This excess may be due to the annihilation or decay of hypothetical dark matter particles or, alternatively, to the contribution of the nearest pulsars. The measured positron-to-antiproton flux ratio is virtually independent of energy from 60 to 400 GeV. This can be understood if the observed local spectra of positrons and antiprotons in the range of tens to hundreds of GeV are formed by the same source. Fast-moving pulsars form pulsar wind nebulae with bow shocks (BSPWNe), which accelerate both the positrons and electrons of the pulsar wind and the hadrons and leptons of galactic CRs from the interstellar medium via the Fermi acceleration mechanism in colliding flows. Such a system can produce identical particle spectra regardless of the site of particle injection. The nearest to the Earth millisecond pulsar PSR J0437-4715 forms a pulsar wind nebula (PWN) with a bow shock observable in optical and ultraviolet wavelengths. This BSPWN is a possible candidate for the main near-Earth ``factory'' of antiparticles along with the Geminga PWN. Considering PSR J0437-4715, we provide the Monte Carlo simulations of particle acceleration in its BSPWN and the analytical model of anisotropic diffusion in the local interstellar medium. We show that this pulsar's contribution can explain the observed positron flux from 30 GeV to 1 TeV, and simultaneously the antiproton flux at hundreds of GeV with an almost energy-independent positron-to-antiproton flux ratio using $\sim 25\%$ of the PSR J0437-4715 pulsar wind power to accelerate positrons and electrons and re-accelerate antiprotons.