The Contribution of Fermi Gamma-Ray Pulsars to the local Flux of Cosmic-Ray Electrons and Positrons

TL;DR

This paper assesses how gamma-ray pulsars detected by Fermi-LAT contribute to local cosmic-ray electrons and positrons, estimating their impact in the 100 GeV to 1 TeV energy range and identifying key pulsars influencing this flux.

Contribution

It provides new distance estimates for Fermi gamma-ray pulsars and models their contribution to local cosmic-ray e+e- flux, highlighting the significance of certain pulsars.

Findings

10 Fermi pulsars significantly contribute to e+e- flux between 100 GeV and 1 TeV.

Some undetected radio pulsars could also contribute if nearby and of certain age.

Fermi-LAT pulsars are more likely to contribute than known radio pulsars in certain parameter spaces.

Abstract

We analyze the contribution of gamma-ray pulsars from the first Fermi-Large Area Telescope (LAT) catalogue to the local flux of cosmic-ray electrons and positrons (e+e-). We present new distance estimates for all Fermi gamma-ray pulsars, based on the measured gamma-ray flux and pulse shape. We then estimate the contribution of gamma-ray pulsars to the local e+e- flux, in the context of a simple model for the pulsar e+e- emission. We find that 10 of the Fermi pulsars potentially contribute significantly to the measured e+e- flux in the energy range between 100 GeV and 1 TeV. Of the 10 pulsars, 2 are old EGRET gamma-ray pulsars, 2 pulsars were discovered with radio ephemerides, and 6 were discovered with the Fermi pulsar blind-search campaign. We argue that known radio pulsars fall in regions of parameter space where the e+e- contribution is predicted to be typically much smaller than from those regions where Fermi-LAT pulsars exist. However, comparing the Fermi gamma-ray flux sensitivity to the regions of pulsar parameter space where a significant e+e- contribution is predicted, we find that a few known radio pulsars that have not yet been detected by Fermi can also significantly contribute to the local e+e- flux if (i) they are closer than 2 kpc, and if (ii) they have a characteristic age on the order of one mega-year.