Energy Spectrum of Fast Second Order Fermi Accelerators as Sources of Ultra-High-Energy Cosmic Rays

TL;DR

This paper demonstrates that second order Fermi acceleration in highly turbulent magnetic fields can produce ultra-high-energy cosmic rays, matching observed spectra and composition when propagation effects are included.

Contribution

It introduces a parametrization of non-power-law spectra from second order Fermi acceleration in turbulent fields, explaining ultra-high-energy cosmic rays.

Findings

Accelerates particles to ultra-high energies in turbulent magnetic fields.

Produces spectra consistent with observed cosmic ray data after propagation effects.

Shows the importance of turbulence in enabling fast second order Fermi acceleration.

Abstract

Stochastic acceleration of cosmic rays in second order Fermi processes is usually considered too slow to reach ultra-high energies, except in specific cases. In this paper we present the energy spectrum obtained from second order Fermi acceleration in highly turbulent magnetic fields as e.g.\ found in the outskirts of AGN jets in situations where it can be sufficiently fast to accelerate particles to the highest observed energies. We parametrize the resulting non-power-law spectra and show that these can describe the cosmic ray energy spectrum and mass-composition data at the highest energies if propagation effects are taken into account.