A cosmic Zevatron based on cyclotron auto-resonance

TL;DR

This paper proposes the cyclotron auto-resonance acceleration (CARA) mechanism as a potential process to accelerate particles to ZeV energies in astrophysical environments with strong magnetic fields and intense radiation, explaining ultra-high-energy cosmic rays.

Contribution

It introduces and demonstrates the feasibility of CARA as a booster mechanism for particles to reach ZeV energies in astrophysical events like mergers or supernovae.

Findings

Hydrogen, helium, and iron nuclei can reach ZeV energies via CARA.

CARA can boost pre-accelerated particles in strong magnetic and radiation fields.

Energy gain remains significant even if resonance conditions are slightly missed.

Abstract

A Zevatron is an accelerator scheme envisaged to accelerate particles to ZeV energies (1 ZeV = $10^{21}$ eV). Schemes, most notably the internal shock model, have been proposed to explain the acceleration of ultra-high-energy cosmic-ray (UHECR) particles that have been sporadically detected reaching Earth since 1962. Here, the cyclotron auto-resonance acceleration (CARA) mechanism is tailored and used to demonstrate possible acceleration of particles ejected as a result of violent astrophysical processes such as the merger of a binary system or a supernova explosion. Such events result in emission of highly-energetic particles and ultra-intense beamed radiation. In the simultaneous presence of a super-strong magnetic field, the condition for cyclotron auto-resonance may be met. Thus CARA can act like a {\it booster} for particles pre-accelerated inside their progenitor by shock waves, possibly among other means. As examples, it is shown that nuclei of hydrogen, helium, and iron-56, may reach ZeV energies by CARA, under which conditions the particles, while gyrating around the lines of an ultra-strong magnetic field, also surf on the waves of a super-intense radiation field. When radiation-reaction is taken into account, it is shown that the ZeV energy gained by a particle can fall off by less than an order-of-magnitude if the resonance condition is missed by roughly less than 20\%.