SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY

By D. Caprioli, A. Spitkovsky. 2013

339 citations recorded by the source corpus.

We use two-dimensional and three-dimensional hybrid (kinetic ions–fluid electrons) simulations to investigate particle acceleration and magnetic field amplification at non-relativistic astrophysical shocks. We show that diffusive shock acceleration operates for quasi-parallel configurations (i.e., when the background magnetic field is almost aligned with the shock normal) and, for large sonic and Alfvénic Mach numbers, produces universal power-law spectra ∝p−4, where p is the particle momentum. The maximum energy of accelerated ions increases with time, and it is only limited by finite box size and run time. Acceleration is mainly efficient for parallel and quasi-parallel strong shocks, where 10%–20% of the bulk kinetic energy can be converted to energetic particles and becomes ineffective for quasi-perpendicular shocks. Also, the generation of magnetic turbulence correlates with efficient ion acceleration and vanishes for quasi-perpendicular configurations. At very oblique shocks, ions can be accelerated via shock drift acceleration, but they only gain a factor of a few in momentum and their maximum energy does not increase with time. These findings are consistent with the degree of polarization and the morphology of the radio and X-ray synchrotron emission observed, for instance, in the remnant of SN 1006. We also discuss the transition from thermal to non-thermal particles in the ion spectrum (supra-thermal region) and we identify two dynamical signatures peculiar of efficient particle acceleration, namely, the formation of an upstream precursor and the alteration of standard shock jump conditions.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/95a621aa3e0a573d6497093f82d366f3f978d480

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In Astronomy and Astrophysics

1. A. Spitkovsky
2. D. Caprioli
3. Hyesung Kang
4. M. Brüggen
5. R. Weeren
6. A. Stroe
7. I. Grenier
8. F. Gasperin

In Nuclear and High Energy Physics

1. A. Spitkovsky
2. D. Caprioli
3. I. Grenier
4. J. Black
5. Hyesung Kang
6. M. Brüggen
7. A. Strong
8. R. Weeren

Citations in the corpus

• Diffuse Radio Emission from Galaxy Clusters (2019, background): “Work by Caprioli & Spitkovsky (2014) indicates that the acceleration efficiency of protons is strongly suppressed at such shocks.”
• The Nine Lives of Cosmic Rays in Galaxies (2015, background): “…been explicitly demonstrated in the ab-initio simulations of MHD turbulence and ions by Spitkovsky (2008) for relativistic shocks (relevant to γ-ray bursts and active galactic nuclei) and by Gargaté & Spitkovsky (2012) and Caprioli & Spitkovsky (2014) for non-relativistic shocks, relevant to SNR.”
• SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. II. MAGNETIC FIELD AMPLIFICATION (2014, methodology): “The back-reaction of such self-generated magnetic turbulence on particle scattering is presented in (Caprioli & Spitkovsky 2014b, hereafter Paper III).”