Magnetic Deflections of Ultra-High Energy Cosmic Rays from Centaurus A

TL;DR

This study simulates the trajectories of ultra-high energy cosmic rays from Centaurus A to Earth, analyzing how the Galactic magnetic field influences their deflections across a range of particle rigidities, revealing significant substructure variability.

Contribution

It models cosmic ray deflections using a recent Galactic magnetic field model, exploring the impact of different random realizations and rigidity levels on arrival directions.

Findings

Mean deflection depends mainly on rigidity.

Substructure varies significantly between realizations.

At 2 EV rigidity, distribution may support Cen A as a primary UHECR source.

Abstract

We present the results of a study that simulates trajectories of ultra-high energy cosmic rays from Centaurus A to Earth, for particle rigidities from $E/Z = 2$ EV to 100 EV, i.e., covering the possibility of primary particles as heavy as Fe nuclei with energies exceeding 50 EeV. The Galactic magnetic field is modeled using the recent work of Jansson and Farrar (JF12) which fitted its parameters to match extragalactic Faraday rotation measures and WMAP7 synchrotron emission maps. We include the random component of the GMF using the JF12 3D model for $B_{\rm rand}(\vec{r})$ and explore the impact of different random realizations, coherence length and other features on cosmic ray deflections. Gross aspects of the arrival direction distribution such as mean deflection and the RMS dispersion depend mainly on rigidity and differ relatively little from one realization to another. However different realizations exhibit non-trivial substructure whose specific features vary considerably from one realization to another, especially for lower rigidities. At the lowest rigidity of 2 EV, the distribution is broad enough that it might be compatible with a scenario in which Cen A is the principle source of all UHECRs. No attempt is made here to formulate a robust test of this possibility, although some challenges to such a scenario are noted.