Collisionless Electron–ion Shocks in Relativistic Unmagnetized Jet–ambient Interactions: Non-Thermal Electron Injection by Double Layer

Abstract

The course of non-thermal electron ejection in relativistic unmagnetized electron-ion shocks is investigated by performing self-consistent particle-in-cell simulations. The shocks are excited through the injection of relativistic jet into ambient plasma, leading to two distinct shocks (named as the trailing shock and leading shock) and a contact discontinuity. The Weibel-like instabilities heat the electrons up to approximately half of ion kinetic energy. The double layers formed in the trailing and leading edges then accelerated the electrons by the ion kinetic energy. The electron distribution function in the leading edge shows a clear non-thermal power-law tail which contains ∼ 1% of electrons and ∼ 8% of electron energy. Its power-law index is -2.6. The acceleration efficiency is ∼ 23% by number and ∼ 50% by energy and the power-law index is -1.8 for electron distribution function in the trailing edge. The effect of the dimensionality is examined by comparing results of 3D simulation with 2D ones. It exhibits that the electron acceleration is more efficient in 2D.

Plasmas in Gamma-Ray Bursts: Particle Acceleration, Magnetic Fields, Radiative Processes and Environments

“…Indeed, helical magnetic fields may be important in jet acceleration and collimation (see the following section), and their existence will stimulate turbulence as the jet propagates through the plasma. This scenario differs than that presented in Figure 3, as it includes both reverse and forward shocks, as well as contact discontinuity [111], all provide possible sites for enhancement of magnetic turbulence.…”

Constraining the magnetic field structure in collisionless relativistic shocks with a radio afterglow polarization upper limit in GW 170817

“…On the other hand, 3D PIC simulations of two counter-streaming unmagnetized relativistic electron-ion (or even electronpositron) plasmas find that the magnetic field just behind the shock is predominantly transverse, with a finite component parallel to the shock normal having, on average, |B |/|B| 10 −2 (e.g., Frederiksen et al 2004;Ardaneh et al 2015Ardaneh et al , 2016. Expressing this ratio in terms of the anisotropy parameter, we find |B , f |/|B f | = ξ f (1 + ξ 2 f ) −1/2 0.50 − 0.66 for 0.57 ξ f 0.89, which suggests that the field anisotropy just behind the shock is significantly smaller as compared to that found in those PIC simulations.…”

Importance of Resolving the Spectral Support of Beam-plasma Instabilities in Simulations

“…They typically occur when relativistic, dilute beams propagate through background plasmas. Examples include relativistic jet propagation (Ardaneh et al 2016;Nishikawa et al 2016), gamma-ray bursts (Ramirez-Ruiz et al 2007;Ardaneh et al 2015), collisionless Shocks (Caprioli & Spitkovsky 2013;Sironi et al 2013;Stockem Novo et al 2016), black hole accretion flows (Riquelme et al 2016), and pair beams, induced by TeV-Blazars (Broderick et al 2012;Schlickeiser et al 2012Schlickeiser et al , 2013Chang et al 2014Chang et al , 2016, propagating through the intergalactic medium.…”