An Inhomogeneous Jet Model and Its Application in BL Lacertae Objects

In the inhomogeneous conical jet model, the electron number den- sity and magnetic field strength have a power-law distribution with the distance from the jet apex. This model can interpret successfully the flat-spectrum radio radiation from the core regions of active galactic nuclei. But the existing model calculation suits only the situation when the enclosed angle between the moving direction of a jet and the line of sight is very large, hence, we need to build a formula for calculating the radiation of inhomogeneous conical jets with any viewing angles. It is generally believed that the enclosed angle between the di- rection of jet motion and the line of sight is very small in BL Lac objects. With the extended inhomogeneous jet model, we have made fitting on the observed radio spectra of three BL Lac objects, and obtained the physical parameters, such as the electron number density and magnetic field strength in their jets. The result indicates that the nearest distance of the conical jet from the black hole is determined by the transition frequency of the observed radiation spec- trum, and that the nearest distance between the conical jet and the black hole is approximately the Schwarzschild radius for the three BL Lac objects.