Cosmic Ray Acceleration in Active Galactic Nuclei - On Centaurus A as a possible UHECR Source

Abstract

We discuss a representative selection of particle acceleration mechanisms believed to be operating in Active Galactic Nuclei. Starting from direct electrostatic field acceleration in the vicinity of the black hole up to Fermi-type particle acceleration in the jet and beyond, possible efficiency constraints on the energization of ultra-high energy cosmic rays (UHECR) are evaluated. When paradigmatically applied to Cen A, the following results are obtained: (i) Proton acceleration to energies of $E_c=5\times 10^{19}$ eV and beyond remains challenging and most likely requires the operation of an additional mechanism capable of boosting energetic seed protons up by a factor of $\sim$ten. It is argued that shear acceleration along the large-scale jet in Cen A could be a promising candidate for this. (ii) Heavier elements, like iron nuclei, are more easily accelerated (by, e.g., shocks or direct electrostatic fields) and may not need additional boosting to reach $E\ge E_c$; (iii) If Cen A indeed proves to be an UHECR source, the cosmic ray composition might thus be expected to become heavier above energies of a few times $10^{19}$ eV.

8 pages, one figure; based on invited talk at the JEM-EUSO Workshop, Torino/Italy, December 2008. To appear in Proceedings of the JEM-EUSO Workshop, under publication by UAP Tokyo, Japan

References in corpus (2)

• Faraday Rotation Structure on Kiloparsec Scales in the Giant Radio Lobes of Centaurus A
• On The Heavy Chemical Composition of the Ultra-High Energy Cosmic Rays

Cited by in corpus (3)

• Active Galactic Nuclei as potential Sources of Ultra-High Energy Cosmic Rays
• Statistical Analysis of the Correlation between Active Galactic Nuclei and Ultra-High Energy Cosmic Rays
• Quantum gravity phenomenology at the dawn of the multi-messenger era -- A review