Gamma-ray flares from red giant/jet interactions in AGN

We propose a new self-consistent hydrodynamical model for description of ultra-short flares of TeV blazars by compact magnetized condensations (blobs) produced when red giant stars cross the jet close to the central black hole. Our study includes a hydrodynamical treatment of evolution of the envelope lost by the star in the jet, and its high energy nonthermal emission through different leptonic and hadronic radiation mechanisms. We show that the fragmented envelope of the star can be accelerated to Lorentz factors up to 100 and radiate effectively the available energy in gamma-rays predominantly through proton synchrotron radiation. The model can readily explain the minute-scale TeV flares on top of longer (typical time-scales of days) gamma-ray variability as observed from the blazar PKS 2155−304, and constrain the key parameters of sources such as the mass of the central black hole M_BH ≈ 10^8M\sun, the total jet power L_j ≈ 1.7×10^47 erg=s and the Doppler factor of the gamma-ray emitting blobs δ ≥ 50