On the acceleration of Ultra-High-Energy Cosmic Rays

Abstract

Ultra High Energy Cosmic Rays (UHECRs) hit the Earth's atmosphere with energies exceeding $10^{18}$ eV. This is the same energy as carried by a tennis ball moving at 100 km/h, but concentrated on a sub-atomic particle. UHECRs are so rare (the flux of particles with $E>10^{20}$ eV is 0.5/km${}^2$/century) that only a few such particles have been detected over the past 50 years. Recently, the HiRes and Auger experiments have reported the discovery of a high-energy cut-off in the UHECR spectrum, and Auger has found an apparent clustering of the highest energy events towards nearby active galactic nuclei. Consensus is building that the highest energy particles are accelerated within the radio-bright lobes of these objects, but it remains unclear how this actually happens, and whether the cut-off is due to propagation effects or reflects an intrinsically physical limitation of the acceleration process. The low event statistics presently allows for many different plausible models; nevertheless observations are beginning to impose strong constraints on them. These observations have also motivated suggestions that new physics may be implicated. We present a review of the key theoretical and observational issues related to the processes of propagation and acceleration of UHECRs and proposed solutions.

arXiv comment11 pages, 3 figures. Invited review to appear in the Triennial edition of the Philosophical Transations of the Royal Society A. Final version accepted

References in corpus (12)

• Correlation of the highest energy cosmic rays with nearby extragalactic objects
• First Observation of the Greisen-Zatsepin-Kuzmin Suppression
• Origin and Propagation of Extremely High Energy Cosmic Rays
• Observation of the suppression of the flux of cosmic rays above 4x10^19eV
• On astrophysical solution to ultra high energy cosmic rays
• Upper limit on the cosmic-ray photon flux above 10^19 eV using the surface detector of the Pierre Auger Observatory
• Ultra-High Energy Cosmic Rays from Young Neutron Star Winds
• Astrophysical Origins of Ultrahigh Energy Cosmic Rays
• Ultrahigh Energy Cosmic Rays: The state of the art before the Auger Observatory
• GZK Photons as Ultra High Energy Cosmic Rays
• Cosmic rays from remnants of quasars?
• Inductive acceleration of UHECRs in sheared relativistic jets

Cited by in corpus (6)

• Introduction to the physics of the total cross-section at LHC: A Review of Data and Models
• Time-dependent perpendicular transport of fast charged particles in a turbulent magnetic field
• Non-thermal transient sources from rotating black holes
• Energy Spectrum of Fast Second Order Fermi Accelerators as Sources of Ultra-High-Energy Cosmic Rays
• Acceleration of charged particles from near-extremal rotating black holes embedded in magnetic fields
• QPO-Based Bayesian Constraints on Charged Particle Dynamics Around Magnetized Schwarzschild Black Holes