Particle acceleration at magnetized, relativistic, turbulent shock fronts
Virginia Bresci, Martin Lemoine, L. Grémillet
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 ${\ensuremath{\gamma}}_{\mathrm{sh}}\ensuremath{\simeq}2.7$, magnetization level $\ensuremath{\sigma}\ensuremath{\simeq}0.01$), 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 $dN/d\ensuremath{\gamma}\ensuremath{\propto}{\ensuremath{\gamma}}^{\ensuremath{-}s}$ with $s\ensuremath{\approx}2.5--3.5$. At larger magnetization levels, stochastic acceleration within the preshock turbulence becomes competitive and can even take over shock acceleration.