Caustic-like Structures in UHECR Flux after Propagation in Turbulent Intergalactic Magnetic Fields

TL;DR

This paper investigates how ultra-high-energy cosmic rays (UHECRs) propagate through turbulent intergalactic magnetic fields, revealing caustic-like structures that cause anisotropic flux patterns depending on observer position.

Contribution

It uncovers non-trivial caustic-like patterns in UHECR trajectories in the intermediate propagation regime, which differ from traditional diffusion models.

Findings

Trajectories form caustic-like structures causing anisotropy.

Flux measurements depend on observer's position relative to source.

Deviation from isotropy is significant in the studied regime.

Abstract

UHECR propagation in a turbulent intergalactic magnetic field in the small-angle scattering regime is well understood for propagation distances much larger than the field coherence scale. The diffusion theory doesn't work and unexpected effects may appear for propagation over smaller distances, from a few and up to 10-20 coherence scales. We study the propagation of UHECRs in this regime, which may be relevant for intermediate mass UHECR nuclei and nG scale intergalactic magnetic fields with 1 Mpc coherence scale. We found that the trajectories form a non-trivial caustic-like pattern with strong deviation from isotropy. Thus, measurements of the flux from a source at a given distance will depend on the position of the observer.