Ensemble Fluctuations of the Flux and Nuclear Composition of Ultra-High Energy Cosmic Ray Nuclei

Abstract

The flux and nuclear composition of ultra-high energy cosmic rays depend on the cosmic distribution of their sources. Data from cosmic ray observatories are yet inconclusive about their exact location or distribution, but provide a measure for the average local density of these emitters. Due to the discreteness of the emitters the flux and nuclear composition is expected to show ensemble fluctuations on top of the statistical variations, i.e. "cosmic variance". This effect is strongest for the most energetic cosmic rays due to the limited propagation distance in the cosmic radiation background and is hence a local phenomenon. For the statistical analysis of cosmic ray emission models it is important to quantify the possible level of this variance. In this paper we present a completely analytic method that describes the variation of the flux and nuclear composition with respect to the local source density. We highlight that proposed future space-based observatories with exposures of O(10^6 km^2 sr yr) will attain sensitivity to observe these spectral fluctuations in the cosmic ray energy spectrum at Earth relative to the overall power-law fit.

11 pages, 4 figures, agrees with version published in Phys.Rev. D87 (2013) 023004

References in corpus (9)

• The surface detector array of the Telescope Array experiment
• Trigger and Aperture of the Surface Detector Array of the Pierre Auger Observatory
• Newly-born pulsars as sources of ultrahigh energy cosmic rays
• Searching for a Correlation Between Cosmic-Ray Sources Above 10^{19} eV and Large-Scale Structure
• Cosmogenic photons as a test of ultra-high energy cosmic ray composition
• Variance of the Galactic nuclei cosmic ray flux
• The Centaurus A Ultrahigh-Energy Cosmic Ray Excess and the Local Extragalactic Magnetic Field
• Propagation of Ultra-High-Energy Cosmic Ray Nuclei in Cosmic Magnetic Fields and Implications for Anisotropy Measurements
• Analytic Solutions of Ultra-High Energy Cosmic Ray Nuclei Revisited

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• UHECR Composition Models
• Measurement of the cosmic ray spectrum above $4\times 10^{18}$ eV using inclined events detected with the Pierre Auger Observatory
• Stable laws and cosmic ray physics
• Performance and science reach of POEMMA for ultrahigh-energy particles
• Curious case of the maximum rigidity distribution of cosmic-ray accelerators
• Ensemble fluctuations of the cosmic ray energy spectrum and the intergalactic magnetic field
• Ultra-high energy cosmic rays with UFA-15 source model in Bumblebee gravity theory