Electron slingshot acceleration in relativistic preturbulent shocks explored via emitted photon polarization

TL;DR

This paper investigates electron acceleration mechanisms in relativistic collisionless shocks using simulations, revealing a novel slingshot process and linking photon polarization features to electron dynamics, with implications for plasma physics and astrophysics.

Contribution

It introduces a new slingshot-like electron injection process and connects photon polarization signatures to transient electron dynamics in relativistic shocks.

Findings

Identification of a slingshot-like electron injection process.

Non-monotonic polarization dependence on photon energy.

Photon polarization as a diagnostic for shock dynamics.

Abstract

Transient electron dynamics near the interface of counterstreaming plasmas at the onset of a relativistic collisionless shock (RCS) is investigated using particle-in-cell simulations. We identify a slingshot-like injection process induced by the drifting electric field sustained by the flowing focus of backwards-moving electrons, which is distinct from the well-known stochastic acceleration. The flowing focus signifies the plasma kinetic transition from a preturbulent laminar motion to a chaotic turbulence. We find a characteristic correlation between the electron dynamics in the slingshot acceleration and the photon emission features. In particular, the integrated radiation from the RCS exhibits a counterintuitive non-monotonic dependence of the photon polarization degree on the photon energy, which originates from a polarization degradation of relatively high-energy photons emitted by the slingshot-injected electrons. Our results demonstrate the potential of photon polarization as an essential information source in exploring intricate transient dynamics in RCSs with relevance for earth-based plasma and astrophysical scenarios.