On the efficiency of particle acceleration by rotating magnetospheres in   AGN
  To investigate the efficiency of centrifugal acceleration of particles as a possible mechanism for the generation of ultra-high $\gamma$-ray nonthermal emission from TeV blazars, we study the centrifugal acceleration of electrons by rotating magnetic field lines, for an extended range of inclination angles and determine the maximum Lorentz factors $\gamma_{max}$ attainable by the electrons via this process. {Two principal limiting mechanisms for the particle acceleration, inverse Compton scattering and breakdown of the bead-on-the-wire approximation, are examined. Particles may be centrifugally accelerated up to $\gamma_{max} \simeq 10^8$ and the main limiting mechanism for the $\gamma_{max}$ is the inverse Compton scattering. The energy of centrifugally accelerated particles can be amply sufficient for the generation (via inverse Compton scattering) of the ultra-high energy (up to $20TeV$) gamma emission in TeV blazars. 
Zaza Osmanov, Andria D. Rogava, Gianluigi Bodo