Speaker
Description
Blazars, a subclass of active galactic nuclei (AGN), are known as the strong emission and frequent activities. The blazar PKS 2155-304 is a high synchrotron-peaked BL Lac with redshit $z=0.116$. On 2006 July 28, an extremely remarkable outburst of VHE $\gamma$-ray emission was reported by H.E.S.S from this blazar, with an average flux more than 10 times the quasi-stable-state value. On the other hand, the variability of the extraordinary outburst is as short as ~200 s, leading to the so-called "Doppler factor Crisis". To figure out the origin of this outburst, we focus on a multi-blob model and try to account for both the quasi-stable and flaring states in the blazars in the same framework. In our model, the emission of blazars consists of two components. One component comprises the emission of numerous blobs with weak dissipation along the jet. The other component arises from a few more powerful blobs that could randomly appear in any position of the jet, probably due to stronger dissipation or enhancement of Doppler factor. We show that the model is capable of explaining the quasi-steady state emission and the flaring state emission in terms of both spectrum and lightcurve with a modest Doppler factor. The obtained parameters may shed some lights on properties of the relativistic jet.
