Magnetized Sources of Ultra-high Energy Nuclei and Extragalactic Origin of the Ankle

Abstract

It has recently been suggested that ultra-high energy cosmic rays could have an extragalactic origin down to the "second knee" at ~4x10^{17}eV. In this case the "ankle" or "dip" at ~5x10^{18}eV would be due to pair production of extragalactic protons on the cosmic microwave background which requires an injection spectrum of about E^{-2.6}. It has been pointed out that for injection of a mixed composition of nuclei a harder injection spectrum E^{-2.2} is required to fit the spectra at the highest energies and a galactic component is required in this case to fit the spectrum below the ankle, unless the proton fraction is larger than 85%. Here we perform numerical simulations and find that for sufficiently magnetized sources, observed spectra above 10^{19}eV approach again the case of pure proton injection due to increased path-lengths and more efficient photo-disintegration of nuclei around the sources. This decreases secondary fluxes at a given energy and thus requires injection spectra ~E^{-2.6}, as steep as for pure proton injection. In addition, the ankle may again be sufficiently dominated by protons to be interpreted as a pair production dip.

arXiv comment12 latex pages, 9 ps figures included

References in corpus (22)

• Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
• Origin and Propagation of Extremely High Energy Cosmic Rays
• Particle acceleration by ultra-relativistic shocks: theory and simulations
• Small-scale anisotropy of cosmic rays above 10^19eV observed with the Akeno Giant Air Shower Array
• Interpenetrating plasma shells: near-equipartition magnetic field generation and non-thermal particle acceleration
• Constrained Simulations of the Magnetic Field in the Local Universe and the Propagation of UHECRs
• Dip in UHECR spectrum as signature of proton interaction with CMB
• A Study of the Composition of Ultra High Energy Cosmic Rays Using the High Resolution Fly's Eye
• Measurement of the Cosmic Ray Energy Spectrum and Composition from 10^{17} to 10^{18.3} eV Using a Hybrid Fluorescence Technique
• Models of the Knee in the Energy Spectrum of Cosmic Rays
• Inter-galactic Shock Acceleration and the Cosmic Gamma-ray Background
• Astrophysical Origins of Ultrahigh Energy Cosmic Rays
• Extra-galactic magnetic fields and the second knee in the cosmic-ray spectrum
• Diffusive propagation of UHECR and the propagation theorem
• Mapping deflections of extragalactic Ultra-High Energy Cosmic Rays in magnetohydrodynamic simulations of the Local Universe
• Anti-GZK effect in Ultra High Energy Cosmic Rays diffusive propagation
• The highest-energy cosmic rays
• Ultra-High Energy Heavy Nuclei Propagation in Extragalactic Magnetic Fields
• Cosmic Magnetic Fields and Their Influence on Ultra-High Energy Cosmic Ray Propagation
• Diffusive Shock Acceleration of High Energy Cosmic Rays
• The mass composition of cosmic rays above 10^17 eV
• Ultra-High Energy Cosmic Ray Nuclei from Individual Magnetized Sources

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• The intergalactic propagation of ultra-high energy cosmic ray nuclei
• Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and composition
• SimProp: a Simulation Code for Ultra High Energy Cosmic Ray Propagation
• Cosmogenic photons as a test of ultra-high energy cosmic ray composition
• On The Heavy Chemical Composition of the Ultra-High Energy Cosmic Rays
• The Intergalactic Propagation of Ultra-High Energy Cosmic Ray Nuclei: An Analytic Approach
• Signatures of the extragalactic cosmic-ray source composition from spectrum and shower depth measurements
• Propagation of Ultra-High-Energy Cosmic Ray Nuclei in Cosmic Magnetic Fields and Implications for Anisotropy Measurements
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