Rapid TeV variability in Blazars as result of Jet-Star Interaction

Abstract

We propose a new model for the description of ultra-short flares from 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 simple dynamical model for the 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 or external inverse Compton scattering of electrons. 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. In the framework of the proposed scenario, the key parameters of the source are robustly constrained. In the case of proton synchrotron origin of the emission a mass of the central black hole of $M_{\rm BH}\approx 10^8 M_{\odot}$, a total jet power of $L_{\rm j} \approx 2\times 10^{47} \, \rm erg\,s^{-1}$ and a Doppler factor, of the gamma-ray emitting blobs, of $\delta\geq 40$ are required. Whilst for the external inverse Compton model, parameters of $M_{\rm BH}\approx 10^8 M_{\odot}$, $L_{\rm j} \approx 10^{46} \, \rm erg\,s^{-1}$ and the $\delta\geq 150$ are required.