Publication Date:
2019-11-28
Description:
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 Earths 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 conned) by magnetosonic-whistler waves within the shock transition layer, especially when the shock angle is large ((sub Bn) approximately equal or greater than 70). When measured by the Magnetospheric Multiscale mission at a high cadence, 0.5 keV electron ux increased exponentially in the shock transition layer. However, the ux prole was not entirely smooth and the uctuation showed temporal/spectral association with large-amplitude (B/B ~ 0.3), low-frequency (approximately equal or less than 0.1 (sub ce) where (sub ce) is the cyclotron frequency), obliquely propagating ((sub kB) ~ 3060, where (sub kB) is the angle between the wave vector and background magnetic eld) 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.
Keywords:
Plasma Physics
Type:
GSFC-E-DAA-TN75966
,
The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 886; 1; 53
Format:
text
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