Particle Acceleration in Shearing Flows: Efficiencies and Limits

TL;DR

This paper investigates the efficiency limits of particle acceleration in shearing flows, emphasizing the necessity of relativistic speeds for effective acceleration, and explores implications for cosmic-ray and high-energy astrophysics.

Contribution

It provides estimates of maximum particle energies in relativistic shear flows, highlighting conditions for efficient acceleration in astrophysical jets.

Findings

Relativistic flow speeds are essential for efficient shear acceleration.

Electrons can reach several PeV, protons up to EeV energies in relativistic jets.

Shear acceleration may sustain high-energy electrons and contribute to cosmic rays.

Abstract

We examine limits to the efficiency for particles acceleration in shearing flows, showing that relativistic flow speeds are required for efficient gradual shear acceleration. We estimate maximum achievable particle energies for parameters applicable to relativistic AGN jets. The implications of our estimates is that if large-scale jets are relativistic, then efficient electron acceleration up to several PeV, and proton acceleration up to several EeV energies appears feasible. This suggests that shear particle acceleration could lead to a continued energization of synchrotron X-ray emitting electrons, and be of relevance for the production of ultra-high-energy cosmic-ray particles.