The author presents a model for variability of the flux and polarization of blazars in which turbulent plasma flowing at relativistic speed down a relativistic jet crosses a standing conical shock. The shock compresses the plasma and accelerates electrons to energies up to > 10,000 times their rest-mass energy. The turbulence is simulated as many cells, each with a uniform magnetic field whose direction varies randomly across cells. The density of high-energy electrons and magnitude of the magnetic field in the plasma change randomly with time in a manner that is consistent with the power spectral density of flux variations derived from observations of the blazars 3C 279 and 3C 454.3. The variations in flux and polarization are therefore caused by noise processes rather than by singular events such as explosive injection of energy at the base of the jet.

The results of a number of simulations indicate the range of behavior of flux and polarization versus time that can be produced by such a model. The model allows for short time-scales of optical and gamma-ray variability by restricting the highest-energy electrons radiating at these frequencies to a small fraction of the turbulent cells, perhaps those with a particular orientation of the magnetic field relative to the shock front. Because of this, the volume filling factor at high frequencies is relatively low, while that of the electrons radiating below about 10 THz is near unity. Such a model is consistent with:

  1. the red-noise power spectra of flux variations
  2. shorter time-scales of variability at higher frequencies
  3. frequency dependence of polarization and its variability
  4. breaks in the synchrotron spectrum by more than the radiative loss value of 0.5.

Simulated light curves are generated by a numerical code that currently includes synchrotron radiation as well as inverse Compton scattering of seed photons from both a dust torus and a Mach disk at the jet axis. The latter source of seed photons can produce more pronounced variability in gamma-ray than in optical light curves, as is often observed. This research is supported in part by NASA through Fermi grants NNX08AV65G, NNX10AO59G, NNX11AQ03G, NNX12A079G, and by NSF grant AST-0907893.