Particle Acceleration by Pickup Process Upstream of Relativistic Shocks

Abstract

Particle acceleration at magnetized purely perpendicular relativistic shocks in electron-ion plasmas are studied by means of two-dimensional particle-in-cell simulations. Magnetized shocks with the upstream bulk Lorentz factor ${\gamma }_1\gg 1$ are known to emit intense electromagnetic waves from the shock front, which induce electrostatic plasma waves (wakefield) and transverse filamentary structures in the upstream region via the stimulated/induced Raman scattering and the filamentation instability, respectively. The wakefield and filaments inject a fraction of incoming particles into a particle acceleration process, in which particles are once decoupled from the upstream bulk flow by the wakefield, and are piked up again by the flow. The picked-up particles are accelerated by the motional electric field. The maximum attainable Lorentz factor is estimated as ${\gamma }_{max,e}\sim \alpha {\gamma }_1^3$ for electrons and ${\gamma }_{max,i}\sim (1+m_e{\gamma }_1/m_i){\gamma }_1^2$ for ions, where $\alpha \sim 10$ is determined from our simulation results. $\alpha$ can increase up to ${\gamma }_1$ for weakly magnetized shock if ${\gamma }_1$ is sufficiently large. This result indicates that highly relativistic astrophysical shocks such as external shocks of gamma-ray bursts can be an efficient particle accelerator.

14 pages, 13 figures, accepted to ApJ

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Cited by in corpus (4)

• Linearly-polarized Coherent Emission from Relativistic Magnetized Ion-electron Shocks
• Saturation of the filamentation instability and dispersion measure of Fast Radio Bursts
• Kinetic Simulations of the Filamentation Instability in Pair Plasmas
• Electron density structure measurements with scattered intense laser beam