Pitch-Angle Anisotropy Controls Particle Acceleration and Cooling in Radiative Relativistic Plasma Turbulence

Collisionless Magnetorotational Turbulence in Pair Plasmas: Steady-State Dynamics, Particle Acceleration, and Radiative Cooling

We present 3D fully kinetic shearing-box simulations of pair-plasma magnetorotational turbulence with unprecedented macro-to-microscopic scale separation. While retrieving the expected fluid behavior of the plasma at large scales, we observe a steepening of turbulent spectra at kinetic scales and substantial angular-momentum transport linked with kinetic processes. For the first time, we provide a definitive demonstration of nonthermal particle acceleration in kinetic magnetorotational turbulence agnostically of shearing-box initial conditions by means of a novel strategy exploiting synchrotron cooling.

Radiative Particle-in-Cell Simulations of Turbulent Comptonization in Magnetized Black-Hole Coronae

We report results from the first radiative particle-in-cell simulations of strong Alfvénic turbulence in plasmas of moderate optical depth. The simulations are performed in a local 3D periodic box and self-consistently follow the evolution of radiation as it interacts with a turbulent electron-positron plasma via Compton scattering. We focus on the conditions expected in magnetized coronae of accreting black holes and obtain an emission spectrum consistent with the observed hard state of Cyg X-1. Most of the turbulence power is transferred directly to the photons via bulk Comptonization, shaping the peak of the emission around 100 keV. The rest is released into nonthermal particles, which generate the MeV spectral tail. The method presented here shows promising potential for ab initio modeling of various astrophysical sources and opens a window into a new regime of kinetic plasma turbulence.

Electron Slingshot Acceleration in Relativistic Preturbulent Shocks Explored via Emitted Photon Polarization

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 slingshotlike injection process induced by the drifting electric field sustained by the flowing focus of backward-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 nonmonotonic 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.