Electron Re-acceleration via Ion Cyclotron Waves in the Intracluster Medium

In galaxy clusters, the intracluster medium (ICM) is expected to host a diffuse, long-lived, and invisible population of "fossil" cosmic-ray electrons (CRe) with 1-100 MeV energies. These CRe, if re-accelerated by 100x in energy, can contribute synchrotron luminosity to cluster radio halos...

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Bibliographic Details
Published in:arXiv.org 2023-02
Main Authors: Tran, Aaron, Sironi, Lorenzo, Ley, Francisco, Zweibel, Ellen G, Riquelme, Mario A
Format: Article
Language:English
Subjects:
Cosmic rays
Cyclotrons
Electrons
Galactic clusters
Longitudinal waves
Luminosity
Magnetic pumping
Pitch (inclination)
Scattering
Synchrotrons
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Summary:In galaxy clusters, the intracluster medium (ICM) is expected to host a diffuse, long-lived, and invisible population of "fossil" cosmic-ray electrons (CRe) with 1-100 MeV energies. These CRe, if re-accelerated by 100x in energy, can contribute synchrotron luminosity to cluster radio halos, relics, and phoenices. Re-acceleration may be aided by CRe scattering upon the ion-Larmor-scale waves that spawn when ICM is compressed, dilated, or sheared. We study CRe scattering and energy gain due to ion cyclotron (IC) waves generated by continuously-driven compression in 1D fully kinetic particle-in-cell simulations. We find that pitch-angle scattering of CRe by IC waves induces energy gain via magnetic pumping. In an optimal range of IC-resonant momenta, CRe may gain up to ~10-30% of their initial energy in one compress/dilate cycle with magnetic field amplification ~3-6x, assuming adiabatic decompression without further scattering and averaging over initial pitch angle.
ISSN:2331-8422
DOI:10.48550/arxiv.2209.12902