Anisotropies of ultra-high energy cosmic ray nuclei diffusing from extragalactic sources

TL;DR

This study models the anisotropies in ultra-high energy cosmic ray nuclei arriving from nearby extragalactic sources, predicting dipolar anisotropies of 5-10% around 10 EeV based on diffusion and energy loss effects.

Contribution

It introduces a comprehensive Monte Carlo simulation framework for cosmic ray diffusion, incorporating mixed compositions, energy losses, and magnetic fields to predict anisotropies.

Findings

Dipolar anisotropies of 5-10% at ~10 EeV are predicted.

Anisotropies depend on source density and magnetic field strength.

Heavier compositions dominate above the ankle energy.

Abstract

We obtain the dipolar anisotropies in the arrival directions of ultra-high energy cosmic ray nuclei diffusing from nearby extragalactic sources. We consider mixed-composition scenarios in which different cosmic ray nuclei are accelerated up to the same maximum rigidity, so that $E<ZE_\text{max}^p$, with $Z$ the atomic number and $E_\text{max}^p$ the maximum proton energy. We adopt $E_\text{max}^p\simeq 6$ EeV so as to account for an increasingly heavier composition above the ankle. We obtain the anisotropies through Monte Carlo simulations that implement the cosmic ray diffusion in extragalactic turbulent fields as well as the effects of photo-disintegrations and other energy losses. Dipolar anisotropies at the level of 5 to 10\% at energies $\sim 10$~EeV are predicted for plausible values of the source density and magnetic fields.