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. 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 ∼8% before entering the Galaxy. The amplitude in the [4-8] EeV is only slightly lower ∼5%. The required IGMF is of the order of 5-30 nG, and the UHECR sources must be relatively nearby, within ∼300 Mpc. The absence of a 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 reduces the dipole of these lower-rigidity particles. Photodisintegration of higher-energy UHECRs could also reduce somewhat the lower-energy dipole.
Original language | English |
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Article number | L25 |
Journal | Astrophysical Journal Letters |
Volume | 850 |
Issue number | 2 |
DOIs | |
State | Published - 1 Dec 2017 |
Bibliographical note
Publisher Copyright:© 2017. The American Astronomical Society. All rights reserved.
Keywords
- cosmic rays