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Relativistic electrons generated at Earth's quasi-parallel bow shock
Terry Z Liu1, Vassilis Angelopoulos1, San Lu1
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, USA.
Science Advances
|July 9, 2019
Summary
Quasi-parallel shocks, with foreshock transients, efficiently accelerate electrons to relativistic energies. These previously overlooked structures significantly boost electron acceleration, impacting cosmic ray electron generation.
Area of Science:
- Space physics
- Plasma astrophysics
- High-energy particle acceleration
Background:
- Plasma shocks are key to electron acceleration in space.
- The relative efficiency of quasi-perpendicular versus quasi-parallel shocks in accelerating electrons is debated.
- Recent observations show unexpectedly high relativistic electron energies at quasi-parallel shocks.
Purpose of the Study:
- To investigate the mechanism behind high-energy electron acceleration at quasi-parallel shocks.
- To determine the role of foreshock transients in electron acceleration.
- To compare the electron acceleration efficiency of quasi-parallel and quasi-perpendicular shocks.
Main Methods:
- In situ observations at Earth's bow shock.
- Analysis of electron acceleration through nonlinear structures (foreshock transients).
- Quantification of electron energy gains via betatron acceleration.
Main Results:
- Relativistic electrons are generated by interactions between quasi-parallel shocks and foreshock transients.
- Two stages of betatron acceleration contribute to electron energization.
- Foreshock transients can enhance electron acceleration efficiency by an order of magnitude.
Conclusions:
- Foreshock transients are crucial for efficient electron acceleration at quasi-parallel shocks.
- Quasi-parallel shocks, when interacting with foreshock transients, may be more significant for generating relativistic electrons than previously assumed.
- This finding has implications for understanding the origin of cosmic ray electrons.
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