Observational Properties of Jets in Active Galactic Nuclei

Parsec scale jet properties are shortly presented and discussed. Observational data are used to derive constraints on the jet velocity and orientation, the presence of velocity structures, and the connection between the pc and kpc scale. Two peculiar sources with limb-brightened jets: 1144+35 and Mkn 501 are discussed in detail.Comment: 13 pages with 7 figures. To appear in "Virtual Astrophysical Jets" APSS, Kluwer Academic Publisher - Massaglia, Bodo, Rossi eds - in pres

Stationary relativistic jets

In this paper we describe a simple numerical approach which allows to study the structure of steady-state axisymmetric relativistic jets using one-dimensional time-dependent simulations. It is based on the fact that for narrow jets with vz≈cvz≈c the steady-state equations of relativistic magnetohydrodynamics can be accurately approximated by the one-dimensional time-dependent equations after the substitution z=ctz=ct. Since only the time-dependent codes are now publicly available this is a valuable and efficient alternative to the development of a high-specialised code for the time-independent equations. The approach is also much cheaper and more robust compared to the relaxation method. We tested this technique against numerical and analytical solutions found in literature as well as solutions we obtained using the relaxation method and found it sufficiently accurate. In the process, we discovered the reason for the failure of the self-similar analytical model of the jet reconfinement in relatively flat atmospheres and elucidated the nature of radial oscillations of steady-state jets

Jet speeds in FRI and FRII radio sources

Analytical relations between the mean jet speed and the mean jet flux asymmetry and between their variances are derived in the context of a unified scheme. The mean jet speeds of classical double radio sources axe estimated by using the asymmetry of jet-counter-Jet flux densities taken from the 3CRR and B2 samples. For FRI radio sources the mean jet speed is similar to 0.54 +/- 0.03c, while for FRII low-redshift radio galaxies and intermediate-redshift quasars the values found are similar to 0.4c +/- 0.06c and greater than or equal to 0.6c respectively