http://arxiv.org/abs/1311.0936
The second order Fermi acceleration (Fermi-II) driven by turbulences may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolutions of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from radio to X-ray. The photon spectrum in GeV energy range of Mrk 421 is hard to be fitted by synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of $4.9 \times 10^{38}~\mbox{erg}~\mbox{s}^{-1}$, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.
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