Distortion of Ultra-high-energy sky by Galactic Magnetic Field

TL;DR

This paper examines how Galactic magnetic fields deflect ultra-high-energy protons, affecting their apparent source positions and the potential for source correlation studies, with implications for understanding galactic magnetic structures.

Contribution

It compares four GMF models to analyze UHECR deflections and identifies directions with minimal deflection, aiding source correlation efforts.

Findings

UHE protons near Galactic center are highly deflected (>8°)

Certain directions, like toward Centaurus A, have minimal deflection (<1°) in some models

Northern hemisphere is more suitable for source correlation studies

Abstract

We investigate the deflections of UHE protons by Galactic magnetic field(GMF) using four conventional GMF models in order to discuss the positional correlation between the arrival distribution of UHECRs and their sources. UHE protons coming from the direction around the Galactic center are highly deflected above $8^{\circ}$ by the dipole magnetic field during their propagation in Galactic space. However, in bisymmetric spiral field models, there are directions with the deflection angle below $1^{\circ}$. One of these directions is toward Centaurus A, the nearest radio-loud active galactic nuclei that is one of possible candidates of UHECR sources. On the other hand, UHE protons arriving from the direction of the anti-Galactic center are less deflected, especially in bisymmetric spiral field models. Thus, the northern hemisphere, not including the Galactic center, is suitable for the studies of correlation with sources. The dependence on model parameters is also investigated. The deflection angles of UHE protons are dependent on the pitch angle of the spiral field. We also investigate distortion of the supergalactic plane by GMF. Since the distortion in the direction around Galactic center strongly depends on the GMF model, we can obtain information on GMF around Galactic center if Pierre Auger Observatory finds the significant positional correlation around the supergalactic plane.