Radio Compact Structure In OQ 208

GPS ( GHz-peaked spectrum ) sources have become one important subclass of compact radio sources. The study of GHz-peaked spectrum sources has generated a lot of interest over the last four decades, since these objects offer a unique opportunity to probe both the early evolutionary of relativistic AGN jets and their immediate nuclear environments. The radio source OQ208 (1404+286,Mkn668) is one of the closest GPS sources. The 15 GHz VLBI observations discovered a weak core located between the two mini-lobes and confirmed that OQ 208 is a CSO(Compact Structure Object). In the light of the newly detected proper motions in two lobes of OQ 208, we introduced the Doppler effect into the fit to the observed spectral turnovers and explained the asymmetric flux density of two components in OQ 208.It shows that two models which contain the same beaming parameters but have quite different absorption mechanisms can fit the spectra of the two lobes equally well. In the FFA+Beaming model, the intrinsic emission of two lobes is the optically thin synchrotron emission and the emission of the two lobes suffers different FFA(Free-Free Absorption). So the FFA absorber may be in a more or less spherically symmetric distribution, for example the clouds in the Narrow Line Region. In the SSA+Beaming model, the intrinsic emission of two lobes is synchrotron emission with self-absorption and the emission from the SW lobe further suffers an extra FFA. As such, the absorbing plasma could be distributed in a disk or torus perpendicular to the jet, which just obscured the receding SW lobe emission. In both models, the intrinsic radio spectra and the radio flux densities of the two lobes are assumed to be same. The rationality of this assumption has been discussed in the thesis. At present, it is difficult to decide which model is better. Because the expected fluxes at lower frequencies are significantly different, future high-resolution observations at lower frequencies will be crucial in distinguishing between two models. However, the beaming effects in both models are nearly the same no matter which absorption mechanism is invoked. The advance speed of the lobes is about 0.33c and the inclination angle of the radio jet is around 33o. If the advance speed of the lobe is a constant, the radio activity age in the compact region of OQ208 is about 92 years. If this is confirmed, OQ208 would be the youngest CSO known so far. Basing on the assumption that the SSA+Beaming model is correct, we estimate some parameters, such as the magnetic field, mass in the lobes and so on.