Unveiling the Mechanisms of Electron Energy Spectrum Evolution

TL;DR

This paper models the evolution of the electron energy spectrum using a spatially dependent propagation model with two diffusion regions, revealing a three-segment power-law structure influenced by cooling and diffusion effects from nearby and distant sources.

Contribution

It introduces a novel SDP model with two diffusion regions, providing a comprehensive depiction of electron spectrum evolution under a unified propagation framework.

Findings

Three-segment power-law spectrum identified

Cooling effects dominate below and above TeV energies

Diffusion effects dominate from tens of GeV to TeV

Abstract

The electron spectrum exhibits a complex structure and has controversially proposed origins. This work reproduce the evolution of the electron spectrum based on a spatially dependent propagation (SDP) model. The key point is that our SPD model features two diffusion regions leading to two diffusion timescales, competing with the cooling timescale. This results in a three-segment power-law electron spectrum: (1) The spectrum below tens of GeV is primarily influenced by cooling effects from distant sources. (2) The spectrum dominated by diffusion effects from nearby sources from tens of GeV to TeV. (3) The spectrum above TeV, which is predominantly governed by cooling effects from nearby sources. This evolution is unique to the SDP model, and we offer a comprehensive and clear depiction of electron evolution under a single propagation scenario for the first time.