Ultra-High Energy Cosmic-Ray Acceleration in the Jet of Centaurus A

TL;DR

This paper investigates the maximum energies nuclei can attain through shock acceleration in Centaurus A's jet, considering magnetic fields and spatial constraints, to understand the origin of ultra-high energy cosmic rays.

Contribution

It provides a detailed model of particle acceleration in Cen A's jet, estimating maximum energies for nuclei and neutrinos, aiding in identifying cosmic ray sources.

Findings

Protons can reach 10^{19}-10^{20} eV energies.

Iron nuclei can be accelerated up to 10^{21} eV.

Predicted neutrino energies are consistent with observational constraints.

Abstract

We evaluate the achievable maximum energy of nuclei diffusively accelerated by shock wave in the jet of Cen A, based on an updated model involving the stochastic magnetic fields that are responsible for recent synchrotron X-ray measurements. For the maximum energy analysis, conceivable energy constraints from spatiotemporal scales are systematically considered for the jet-wide including discrete X-ray knots. We find that in the inner region within ~1 arcmin from galactic core, which includes knots AX and BX, proton and iron nucleus can be accelerated to 10^{19}-10^{20} and 10^{21} eV (10-100 EeV and ZeV) ranges, respectively. The upper cutoff energy of the very energetic neutrinos produced via photopion interaction is also provided. These are essential for identifying the acceleration site of the ultra-high energy cosmic ray detected in the Pierre Auger Observatory, which signifies the arrival from nearby galaxies including Cen A.