# Ultrahigh-energy Cosmic-ray Nuclei from Black Hole Jets: Recycling Galactic Cosmic Rays through Shear Acceleration

## TL;DR

This paper models how shear acceleration in active galactic nuclei jets can reaccelerate galactic cosmic rays to ultrahigh energies, producing a hard spectrum and explaining observed composition and anisotropy.

## Contribution

It introduces a Monte Carlo simulation of shear acceleration in AGN jets, demonstrating its effectiveness in producing ultrahigh-energy cosmic rays with specific spectral and compositional features.

## Key findings

- Reacceleration yields a hard cosmic ray spectrum ($E^{-1}$ to $E^0$).
- High-energy nuclei abundance is enhanced due to TeV-PeV injections.
- Model aligns with observed cosmic ray spectrum, composition, and anisotropy data.

## Abstract

We perform Monte Carlo simulations of transrelativistic shear acceleration dedicated to a jet-cocoon system of active galactic nuclei. A certain fraction of galactic cosmic rays in a halo is entrained, and sufficiently high-energy particles can be injected to the reacceleration process and further accelerated up to 100 EeV. We show that the shear reacceleration mechanism leads to a hard spectrum of escaping cosmic rays, $dL_E/dE\propto E^{-1}-E^0$, distinct from a conventional $E^{-2}$ spectrum. The supersolar abundance of ultrahigh-energy nuclei is achieved due to injections at TeV-PeV energies. As a result, we find that the highest-energy spectrum and mass composition can be reasonably explained by our model without contradictions with the anisotropy data.