Cosmic Rays in the Inner Galaxy and the Diffusion Properties of the Interstellar Medium

TL;DR

This paper investigates how cosmic ray propagation differs in the Inner Galaxy compared to local regions, suggesting more turbulent interstellar medium causes a flatter cosmic ray spectrum and different diffusion properties.

Contribution

It proposes that the anomalous diffusion parameter alpha is lower in the Inner Galaxy, explaining the observed spectral differences in cosmic rays.

Findings

Cosmic ray spectrum in the Inner Galaxy is flatter than locally.

Diffusion in the Inner Galaxy is more turbulent, with lower alpha values.

Spectral exponent gamma differs by about 0.1 between regions.

Abstract

Recent measurements of cosmic gamma ray intensities up to TeV energies have been used to estimate the spectral shape of the parent cosmic ray particles present in the interstellar medium. The case is made for the particle spectrum in the Inner Galaxy being flatter than locally and in the Outer Galaxy. Of various possible explanations we make the case for the propagation of the particles being different in the more turbulent interstellar medium of the Inner Galaxy. The characteristic parameter alpha for the so called anomalous diffusion is expected to be less in the Inner Galaxy than that locally and the corresponding power law spectral exponent of the cosmic ray particles gamma will differ from that locally. Arguments are presented favouring a value of alpha lower than the local one by about Delta alpha = 0.2, the consequence is that Delta gamma = 0.1 for the parent particles.