Origin and propagation of the highest energy cosmic rays

TL;DR

This paper reviews shock acceleration and cosmic ray interactions, suggesting that classical astrophysical sources like radio galaxies likely explain the highest energy cosmic rays, but more data is needed for certainty.

Contribution

It provides an overview of cosmic ray acceleration and propagation, arguing against exotic models and emphasizing the potential of radio galaxies as sources.

Findings

Shock acceleration at radio galaxies can explain current data

Exotic models like topological defects are unnecessary

More data needed for definitive origin identification

Abstract

In this lecture I give an overview of shock acceleration, interactions of high energy cosmic rays with, and propagation through, the background radiation, and the resulting electron-photon cascade. I argue that while the origin of the highest energy cosmic rays is still uncertain, it is not necessary to invoke exotic models such as emission by topological defects to explain the existing data. It seems likely that shock acceleration at Fanaroff-Riley Class II radio galaxies can account for the existing data. However, new cosmic ray data, as well as better estimates of the extragalactic radiation fields and magnetic fields will be necessary before we will be certain of the origin of the highest energy particles occurring in nature.