Anisotropies of Ultra-high Energy Cosmic Rays Dominated by a Single Source in the Presence of Deflections

Abstract

This work presents a scenario of ultra-high energy cosmic ray source distribution where a nearby source is solely responsible for the anisotropies in arrival directions of cosmic rays while the rest of the sources contribute only isotropically. An analytical approach focused on large-scale anisotropies, which are influenced by deflections in a Kolmogorov-type turbulent magnetic field, is employed to provide more general results. When the recent Pierre Auger Observatory angular power spectrum above 8 EeV is used the restricted model gives, under the assumption of the small angle approximation, a solution where the RMS deflection with respect to the line of sight is ${\alpha }_{\mathrm{rms}}={\left(50_{-10}^{+11}\right)}^{\circ }$, while the relative flux from the single source $\eta =0.03\pm 0.01$. Furthermore, the solution can be translated into constraints on the source distance, luminosity, and extra-galactic magnetic field strength. For Centaurus A and the Virgo cluster the required relation between the coherence length and the RMS magnetic field strength is obtained: a coherence length of $\sim 100\mathrm{kpc}$ would imply the RMS field strength around $1\mathrm{nG}$ for iron dominated and above $10\mathrm{nG}$ for proton dominated composition. We also performed trajectory simulations with our publicly available code CRPropa to show that our analytical model can serve as a good approximation as long as the deflections in cosmic magnetic fields can be described as a random walk. The simulations showed that generally structured fields tend to suppress large-scale anisotropies, especially the dipole, compared to anisotropies at smaller scales described by higher multipoles.

27 pages, 15 figures

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Cited by in corpus (8)

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• Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies
• Detecting ultra-high energy cosmic ray anisotropies through cross-correlations
• Ultrahigh-energy dipole and beyond
• Predictions for the flux of high-energy cosmogenic neutrinos and the influence of the extragalactic magnetic field
• Ultra-high-energy Cosmic Ray Sources can be Gamma-ray Dim
• Prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic rays from a nearby source with the K-EUSO orbital telescope
• Combined Fit of Spectrum and Composition for FR0 Radio-galaxy-emitted Ultra-high-energy Cosmic Rays with Resulting Secondary Photons and Neutrinos