Gamma-Ray Astronomy of Cosmic Rays

TL;DR

Gamma-ray astronomy provides crucial insights into cosmic ray origins and propagation, with recent observational advances supporting supernova remnants as sources and informing diffuse background models.

Contribution

The paper reviews recent progress in gamma-ray observations of cosmic rays, highlighting the potential resolution of key astrophysical questions and discussing the H.E.S.S. telescope array.

Findings

Progress in gamma-ray observations supports supernova remnants as sources.

Observations are nearing resolving the diffuse gamma-ray background contributions.

Instrumental sensitivities are improving, enabling new astrophysical insights.

Abstract

Many of the basic problems in the astrophysics of charged Cosmic Rays remain on principle unresolved by in situ observations in the Solar System due to the chaotic nature of the propagation of these particles in Interstellar space. This concerns the existence and the nature of localized individual particle sources as well as the transport in the Galaxy and establishes the need for astronomical observations of secondary gamma-rays. The only exception may be the highest energy particles at energies around $10^{20}$ eV which possibly reach us on straight line orbits from their production sites. Recently such gamma-ray observations, both in space and on the ground, have made great progress even though the instrumental sensitivities are still low. It is argued that two basic questions, regarding first of all the Supernova Remnant source hypothesis and secondly the contributions to the diffuse gamma-ray background, have come close to an empirical resolution. Apart from motivations deriving from extragalactic astronomy this expectation is at the root of the construction of a new generation of high-sensitivity gamma-ray instruments. As a representative example the H.E.S.S. array of atmospheric Cherenkov telescopes is described.