Stochastic shock drift acceleration in the shock transition region with finite pitch-angle anisotropy
Abstract
The acceleration of cosmic rays is one of the important subjects in astrophysics. Galactic cosmic rays are believed to be accelerated by the first order Fermi acceleration (e.g. Drury 1983) at supernova remnant (SNR) shocks. However, since this acceleration process is not efficient for non-relativistic electrons (with energies below 1 MeV), an alternative particle acceleration process is needed to inject thermal electrons to mildly relativistic energies to explain observed electron fluxes at SNRs. This is called the electron injection problem and has been a subject of extensive research over the decades.
We proposed the stochastic shock drift acceleration as a plausible acceleration model of non-relativistic electrons (Katou and Amano 2019). This model takes into account both the adiabatic shock drift acceleration (Wu 1984, Leroy and Mangeney 1984) in the shock transition region and a stochastic pitch-angle scattering by electromagnetic waves. We theoretically analyzed this model in the limit of strong scatterings by using a simple box model which considers only the dependence on energy. We showed that this model reproduces a power-law energy spectrum consistent with in-situ observations at the Earth's bow shock. We also found that there appears a high-energy cutoff in the power-law spectrum. The scaling law of this cutoff energy with respect to the shock velocity indicates that it can accelerate electrons up to about 1 MeV at SNR shocks, which is sufficient for injection into the first order Fermi process. We will also present an extension of the theory to include the effect of finite pitch-angle anisotropy, which may affect the spectrum near the cutoff energy.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH23B3390K
- Keywords:
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- 7829 Kinetic waves and instabilities;
- SPACE PLASMA PHYSICS;
- 7845 Particle acceleration;
- SPACE PLASMA PHYSICS;
- 7846 Plasma energization;
- SPACE PLASMA PHYSICS;
- 7851 Shock waves;
- SPACE PLASMA PHYSICS