A Galactic Cosmic Ray Electron Spectrum from 2 MeV to 2 TeV That Fits Voyager 5-60 MeV Data at Low Energies and PAMELA and AMS-2 Data at 10 GeV Using an Electron Source Spectrum E^-2.25 A Calculation Using a Monte Carlo Diffusion Model

TL;DR

This paper models the galactic cosmic ray electron spectrum from MeV to TeV energies using a Monte Carlo diffusion approach, fitting data from Voyager, PAMELA, FERMI, and AMS-2, and suggests a single spectral break in diffusion.

Contribution

It introduces a unified model fitting electron spectra over five orders of magnitude with a single diffusion coefficient break and a source spectrum with a steepening at high energies.

Findings

Source spectral index = -2.25 below 10 GeV

Spectrum steepens to -2.40 at highest energies

Galaxy acts as a calorimeter for electrons in 0.1-10 GeV range

Abstract

In this paper we fit the observed galactic cosmic ray electron spectrum from a few MeV to 1 TeV. New data from Voyager from 5-60 MeV beyond the heliopause is used along with high energy data from the PAMELA, FERMI and AMS-2 instruments in Earth orbit. Using a Monte Carlo diffusion model for galactic propagation we obtain a source rigidity spectrum with a spectral index =-2.25 independent of energy below 10 GeV, possibly steepening above 10 GeV to 2.40 at the highest energies. This spectrum will fit the electron data over 5 orders of magnitude to within + 10% at both low and high energies. This steepening of the electron source spectrum could be an important feature of the acceleration process, e.g., synchrotron loss during acceleration could steepen the source spectrum. This fit requires only a single break in the rigidity dependence of the diffusion coefficient by ~1.0 power in the exponent at about 1.0 GV. The calculations also predict the distribution of electrons perpendicular to the galactic disk. The galaxy does act as a calorimeter for electrons in the energy range 0.1-10 GeV where ~80% of the electrons are trapped. At higher energies the electrons escape the galactic disk rapidly. At energies ~1 TEV the electrons loose most of their energy by synchrotron and inverse Compton emission within < 0.5 Kpc of their origin near the galactic equator. At energies < 0.1 GeV, because of the increase in the diffusion coefficient below ~1 GV, and the absence of other significant loss processes, the electrons escape and form a difficult to detect, but important galactic halo population.