Relativistic electrons generated at Earth's quasi-parallel bow shock.

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.