The extragalactic ultra-high energy cosmic-ray dipole

Abstract

We explore the possibility that the recently detected dipole anisotropy in the arrival directions of~$>8$~EeV ultra-high energy cosmic-rays (UHECRs) arises due to the large-scale structure (LSS). We assume that the cosmic ray sources follow the matter distribution and calculate the flux-weighted UHECRs' RMS dipole amplitude taking into account the diffusive transport in the intergalactic magnetic field (IGMF). We find that the flux-weighted RMS dipole amplitude is $\sim 8$% before entering the Galaxy. The amplitude in the [4-8] EeV is only slightly lower $\sim 5$%. The required IGMF is of the order of {5-30 nG}, and the UHECR sources must be relatively nearby, within $\sim$300 Mpc. The absence of statistically significant signal in the lower energy bin can be explained if the same nuclei specie dominates the composition in both energy bins and diffusion in the Galactic magnetic field (GMF) reduces the dipole of these lower rigidity particles. Photodisintegration of higher energy UHECRs could also reduce somewhat the lower energy dipole.

arXiv comment6 pages, 5 figures, accepted in ApJ Letters

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• The Imprint of Large Scale Structure on the Ultra-High-Energy Cosmic Ray Sky
• What can be learnt from UHECR anisotropies observations? Paper I : large-scale anisotropies and composition features
• Cosmic-Ray Anisotropy from Large Scale Structure and the effect of magnetic horizons
• Cosmic ray $e^{+}{e}^{-}$ spectrum excess and peak feature observed by the DAMPE experiment from dark matter
• Large-scale cosmic ray anisotropies with 19 years of data from the Pierre Auger Observatory
• Constraints on UHECR sources and extragalactic magnetic fields from directional anisotropies
• UHECR mass composition at highest energies from anisotropy of their arrival directions
• Ultra High Energy Cosmic Ray Source Models: Successes, Challenges and General Predictions
• Ultrahigh-energy dipole and beyond
• Treasure Maps for Detections of Extreme Energy Cosmic Rays
• Searching for All-Scale Anisotropies in the Arrival Directions of Cosmic Rays above the Ankle
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