The Centaurus A Ultrahigh-Energy Cosmic Ray Excess and the Local Extragalactic Magnetic Field

TL;DR

This paper investigates the excess of ultrahigh-energy cosmic rays near Centaurus A, suggesting that if Cen A is the source, the local extragalactic magnetic field must be stronger than previously thought, impacting cosmic ray propagation models.

Contribution

It provides new constraints on the local extragalactic magnetic field strength based on cosmic ray anisotropy observations around Centaurus A.

Findings

EGMF strength > 20 nG within several Mpc if Cen A is the source

The excess could be a statistical anomaly or indicate a stronger EGMF

Implications for cosmic ray scattering, time delays, and magnetic lensing

Abstract

The ultrahigh-energy cosmic-ray anisotropies discovered by the Pierre Auger Observatory give the potential to finally address both the particles' origins and properties of the nearby extragalactic magnetic field (EGMF). We examine the implications of the excess of ~ 10^20 eV events around the nearby radio galaxy Centaurus A. We find that, if Cen A is the source of these cosmic rays, the angular distribution of events constrains the EGMF strength within several Mpc of the Milky Way to > 20 nG for an assumed primary proton composition. Our conclusions suggest that either the observed excess is a statistical anomaly or the local EGMF is stronger then conventionally thought. We discuss the implications of this field, including UHECR scattering from more distant sources, time delays from transient sources, and the possibility of using magnetic lensing signatures to attain tighter constraints.