  We report results from the first radiative particle-in-cell simulations of
strong Alfvenic 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.
