Plasma kinetic effects in relativistic radiation mediated shocks

Abstract

Fast shocks that form in optically thick media are mediated by Compton scattering and, if relativistic, pair creation. Since the radiation force acts primarily on electrons and positrons, the question arises of how the force is mediated to the ions which are the dominant carriers of the shock energy. It has been widely thought that a small charge separation induced by the radiation force generates electric field inside the shock that decelerates the ions. In this paper we argue that, while this is true in sub-relativistic shocks which are devoid of positrons, in relativistic radiation mediated shocks (RRMS), which are dominated by newly created $e^{+}{e}^{-}$ pairs, additional coupling is needed, owing to the opposite electric force acting on electrons and positrons. Specifically, we show that dissipation of the ions energy must involve collective plasma interactions. By constructing a multi-fluid model for RRMS that incorporates friction forces, we estimate that momentum transfer between electrons and positrons (and/or ions) via collective interactions on scales of tens to thousands proton skin depths, depending on whether friction is effective only between $e^{+}{e}^{-}$ pairs or also between pairs and ions, is sufficient to coupe all particles and radiation inside the shock into a single fluid. This leaves open the question whether in relativistic RMS particles can effectively accelerate to high energies by scattering off plasma turbulence. Such acceleration might have important consequences for relativistic shock breakout signals.

8 pages, 3 figures

References in corpus (7)

• On the structure of relativistic collisionless shocks in electron-ion plasmas
• Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks: Electron-Positron Plasmas
• Relativistic Radiation Mediated Shocks
• Relativistic Photon Mediated Shocks
• Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime
• Monte-Carlo simulations of relativistic radiation mediated shocks: II. photon starved regime
• Radiation-mediated shocks: kinetic processes and transition to collisionless shocks

Cited by in corpus (8)

• Microphysics of Relativistic Collisionless Electron-ion-positron Shocks
• Particle Acceleration in Mildly Relativistic Outflows of Fast Energetic Transient Sources
• An efficient method for fitting radiation-mediated shocks to gamma-ray burst data: The Kompaneets RMS approximation
• Observational characteristics of radiation-mediated shocks in photospheric gamma-ray burst emission
• The role of plasma instabilities in relativistic radiation mediated shocks: stability analysis and particle-in-cell simulations
• Breakdown of force-free electrodynamics in electric zones
• Magnetically driven coupling in relativistic radiation-mediated shocks
• Anomalous coupling in radiation mediated shocks}