Black-Hole Engine Kinematics, Flares from PKS 2155-304, and   Multiwavelength Blazar Analysis
  Kinematical and luminosity relations for black-hole jet sources are reviewed. If the TeV flares observed from PKS 2155-304 in 2006 July are assumed to originate from a black hole with mass $\approx 10^8 M_8 M_\odot$, then the $\sim 5$ minute variability timescale is consistent with the light-travel time across the Schwarzschild radius of the black hole if $M_8\sim 1$. The absolute jet power in a synchrotron/SSC model exceeds, however, the Eddington luminosity for a black hole with $M_8\sim 1$ unless the jet is highly efficient. The maximum Blandford-Znajek power is $\sim 10^{46}M_8$ ergs s$^{-1}$ if the magnetic-field energy density threading the horizon is equated with the luminous energy density in the vicinity of the black hole. An external Compton component can relax power requirements, so a black hole with mass $\sim 10^8 M_\odot$ could explain the observed flaring behavior. For the Swift and HESS data taken in 2006 July, relativistic outflows with bulk Lorentz factor $\Gamma \gtrsim 30$ satisfy $\gamma$-$\gamma$ attenuation limits. If this system harbors a binary black hole, then the accretion disk from a more massive, $\sim 10^9 M_\odot$ black-hole primary would make an additional external radiation component. Dual thermal accretion disk signatures would confirm this scenario. 
Charles D. Dermer, Justin D. Finke, and Govind Menon