Towards extracting cosmic magnetic field structures from cosmic-ray arrival directions

TL;DR

This paper introduces a new likelihood-based method to analyze ultra-high energy cosmic-ray arrival directions, aiming to detect coherent magnetic field structures and infer the Galactic magnetic field component perpendicular to the line of sight.

Contribution

The paper presents a novel statistical approach that models cosmic-ray alignments to extract magnetic field information directly from cosmic-ray data.

Findings

Method can distinguish between isotropic and structured cosmic-ray patterns.

Sensitivity tested with astrophysical simulations shows promising discriminative power.

Approximates local magnetic deflections via a fitted vector field.

Abstract

We present a novel method to search for structures of coherently aligned patterns in ultra-high energy cosmic-ray arrival directions simultaneously across the entire sky. This method can be used to obtain information on the Galactic magnetic field, in particular the integrated component perpendicular to the line of sight, from cosmic-ray data only. Using a likelihood-ratio approach, neighboring cosmic rays are related by rotatable, elliptically shaped density distributions and the significance of their alignment with respect to circular distributions is evaluated. In this way, a vector field tangential to the celestial sphere is fitted which approximates the local deflections in cosmic magnetic fields if significant deflection structures are detected. The sensitivity of the method is evaluated on the basis of astrophysical simulations of the ultra-high energy cosmic-ray sky, where a discriminative power between isotropic and signal-induced scenarios is found.