Simultaneous Acceleration of Protons and Electrons at Nonrelativistic Quasiparallel Collisionless Shocks

Jaehong Park, Damiano Caprioli, and Anatoly Spitkovsky
Phys. Rev. Lett. 114, 085003 – Published 27 February 2015

Abstract

We study diffusive shock acceleration (DSA) of protons and electrons at nonrelativistic, high Mach number, quasiparallel, collisionless shocks by means of self-consistent 1D particle-in-cell simulations. For the first time, both species are found to develop power-law distributions with the universal spectral index 4 in momentum space, in agreement with the prediction of DSA. We find that scattering of both protons and electrons is mediated by right-handed circularly polarized waves excited by the current of energetic protons via nonresonant hybrid (Bell) instability. Protons are injected into DSA after a few gyrocycles of shock drift acceleration (SDA), while electrons are first preheated via SDA, then energized via a hybrid acceleration process that involves both SDA and Fermi-like acceleration mediated by Bell waves, before eventual injection into DSA. Using the simulations we can measure the electron-proton ratio in accelerated particles, which is of paramount importance for explaining the cosmic ray fluxes measured on Earth and the multiwavelength emission of astrophysical objects such as supernova remnants, radio supernovae, and galaxy clusters. We find the normalization of the electron power law is 102 of the protons for strong nonrelativistic shocks.

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  • Received 2 December 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.085003

© 2015 American Physical Society

Authors & Affiliations

Jaehong Park, Damiano Caprioli, and Anatoly Spitkovsky

  • Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA

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Vol. 114, Iss. 8 — 27 February 2015

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