Particle acceleration at magnetized, relativistic, turbulent shock fronts

Abstract

The efficiency of particle acceleration at shock waves in relativistic, magnetized astrophysical outflows is a debated topic with far-reaching implications. Here, we study the impact of well-developed turbulence in the pre-shock plasma. Our simulations demonstrate that, for a mildly relativistic magnetized pair shock (Lorentz factor γ_{sh}≃2.7, magnetization level σ≃0.01), strong turbulence can revive particle acceleration in a superluminal configuration that otherwise prohibits it. Depending on the initial plasma temperature and magnetization, shock-drift or diffusive-type acceleration governs particle energization, producing power-law spectra dN/dγ∝γ^{−s} with s≈2.5–3.5. At larger magnetization levels, stochastic acceleration within the preshock turbulence becomes competitive and can even take over shock acceleration.