Effect of the diffusion parameters on the observed gamma-ray spectrum of sources and their contribution to the local all-electron spectrum: the EDGE code

TL;DR

This paper introduces the EDGE code for modeling electron and gamma-ray propagation from nearby pulsar sources, analyzing how diffusion parameters influence observed spectra and contributions to the local electron-positron flux.

Contribution

The paper presents a new computational tool, EDGE, that simulates electron and gamma-ray propagation from sources, allowing detailed analysis of parameter effects on observed spectra.

Findings

Diffusion parameters significantly affect gamma-ray spectra.

Source characteristics influence the local electron-positron flux.

Approximations in modeling can impact spectral predictions.

Abstract

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ($\sim$hundreds of parsecs) and middle age (maximum of $\sim$hundreds of kyr) sources. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat the propagation of electrons and compute their diffusion from a central source with a flexible injection spectrum. Using this code, we can derive the source's gamma-ray spectrum, spatial extension, the all-electron density in space, the electron and positron flux reaching the Earth and the positron fraction measured at the Earth. We present in this paper the foundations of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth. We also studied the effect of several approximations usually performed in these studies.