Synchrotron Self-Compton Model for PKS 2155-304
  H.E.S.S. observed TeV blazar PKS 2155--304 in a strong flare state in 2006 July. The TeV flux varied on timescale as short as a few minutes, which sets strong constraints on the properties of the emission region. By use of the synchrotron self-Compton model, we found that models with the bulk Lorentz factor $\sim 100$, the size of the emission region $\sim 10^{15}$ cm, and magnetic field $\sim 0.1$ G explain the observed spectral energy distribution and the flare timescale $\sim$ a few minutes. This model with a large value of $\Gamma$ accounts for the emission spectrum not only in the TeV band but also in the X-ray band. The major cooling process of electrons/positrons in the jet is inverse Compton scattering off synchrotron photons. The energy content of the jet is highly dominated by particle kinetic energy over magnetic energy. 
M. Kusunose and F. Takahara