Electron scattering by low-frequency whistler waves at earth's bow shock

M. Oka, F. Otsuka, S. Matsukiyo, L. B. Wilson, M. R. Argall, T. Amano, T. D. Phan, M. Hoshino, O. Le Contel, D. J. Gershman, J. L. Burch, R. B. Torbert, J. C. Dorelli, B. L. Giles, R. E. Ergun, C. T. Russell, P. A. Lindqvist

研究成果: ジャーナルへの寄稿学術誌査読

14 被引用数 (Scopus)

抄録

Electrons are accelerated to nonthermal energies at shocks in space and astrophysical environments. While shock drift acceleration (SDA) has been considered a key process of electron acceleration at Earth's bow shock, it has also been recognized that SDA needs to be combined with an additional stochastic process to explain the observed power-law energy spectra. Here, we show mildly energetic (∼0.5 keV) electrons are locally scattered (and accelerated while being confined) by magnetosonic-whistler waves within the shock transition layer, especially when the shock angle is large (θBN ≥ 70°). When measured by the Magnetospheric Multiscale mission at a high cadence, ∼0.5 keV electron flux increased exponentially in the shock transition layer. However, the flux profile was not entirely smooth and the fluctuation showed temporal/spectral association with large-Amplitude (δB/B ∼0.3), low-frequency (≤0.ωce where ωce is the cyclotron frequency), obliquely propagating (θkB ∼30°-60°, where θkB is the angle between the wave vector and background magnetic field) whistler waves, indicating that the particles were interacting with the waves. Particle simulations demonstrate that, although linear cyclotron resonances with ∼0.5 keV electrons are unlikely due to the obliquity and low frequencies of the waves, the electrons are still scattered beyond 90° pitch angle by (1) resonant mirroring (transit-Time damping), (2) non-resonant mirroring, and (3) subharmonic cyclotron resonances. Such coupled nonlinear scattering processes are likely to provide the stochasticity needed to explain the power-law formation.

本文言語英語
論文番号53
ジャーナルAstrophysical Journal
886
1
DOI
出版ステータス出版済み - 11月 20 2019

!!!All Science Journal Classification (ASJC) codes

  • 天文学と天体物理学
  • 宇宙惑星科学

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