Collisionless shocks having relativistic velocities in relativistically hot plasmas

Abstract

Shocks in relativistically hot plasmas are thought to exist in various high-energy astrophysical phenomena, but it is not clear how relativistic collisionless shocks are formed, whether particles are accelerated by the shock as in the case of cold upstream. In this work, collisionless shocks with a relativistic shock velocity in relativistically hot unmagnetized electron-positron plasmas are investigated by two-dimensional particle-in-cell simulations. It is shown that the upstream flow is dissipated by the Weibel instability, so that the relativistic collisionless shock is formed as in the case of cold upstream. The density and magnetic field structures around the shock front are almost independent of the upstream temperature when the spatial scale is normalized by the inertial length scale which takes into account the relativistic temperature. This can be understood by considering the pressure anisotropy, which asymptotically approaches a finite value due to the relativistic beaming effect, even as the temperature becomes relativistically hotter and hotter. In addition, as long as the shock velocity is relativistic, some particles are accelerated, forming a power-law energy spectrum similar to that in the cold upstream.

9 pages, 7 figures

References in corpus (12)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• On the structure of relativistic collisionless shocks in electron-ion plasmas
• Relativistic Collisionless Shocks in Unmagnetized Electron-Positron Plasmas
• Loading Relativistic Maxwell Distributions in Particle Simulations
• Long-term Evolution of Relativistic Unmagnetized Collisionless Shocks
• Origin of intense electron heating in relativistic blast waves
• Interaction of a Relativistic Magnetized Collisionless Shock with a Dense Clump
• Saturation Level of Ion Weibel Instability and Isotropization Length Scale in Electron-Ion Weibel-Mediated Shocks
• Particle acceleration and magnetic field amplification by relativistic shocks in inhomogeneous media
• Collisionless shock in a relativistically hot unmagnetized electron-positron plasma
• Property of downstream turbulence driven by the special relativistic shock-clump interaction