Radiative Turbulence in Magnetically Dominated Plasmas: Particle Acceleration and Cooling

Magnetized turbulence is often invoked to explain the nonthermal emission observed from a wide variety of astrophysical sources. By means of fully-kinetic particle-in-cell simulations that include self-consistently the radiation reaction force, we investigate the acceleration and cooling of particles in turbulent plasmas in the strong cooling regime. This regime is relevant to a variety of high-energy astrophysical phenomena such as the prompt emission of gamma-ray bursts and the gamma-ray flares from the Crab Nebula. We show that reconnecting current sheets, which develop self-consistently in the turbulent plasma, inject particles with a hard power-law distribution and low pitch angle due to the acceleration powered by magnetic-field-aligned electric fields. Particles cool down by increasing their pitch angle, which affects the cooled particle distribution. Due to the low pitch angle of the accelerated particles, significant synchrotron radiation is emitted above the synchrotron burnoff limit, as is required to explain the gamma-ray emission in Crab flares. Synchrotron radiation from the accelerated particles give rise to a synchrotron energy flux with a power-law range $\nu F_\nu \propto \nu^s$ with $s \sim 1$, up to the peak frequency $\nu_{\rm{peak}}$ consistent to the observed prompt emission of gamma-ray bursts. The presented results have also implications for understanding the generation of nonthermal particles in other high-energy astrophysical sources.