New results of instantaneous spectra study confirms an old hypothesis that extragalactic radio sources have a double structure. Instantaneous 1–22 GHz spectra and their long-term variability for VLBI-compact extragalactic objects monitored during 1979–1997 at the RATAN–600 are used. Analysis of these spectra gives that a VLBI-compact continuous jet have to be by a general structure and spectra component of such objects. The observed multi component VLBI-structures are bound to be, as a rule, the brightest regions of such continuos jet. A second component is a relatively extended, optically thin cloud (a lobe or an envelope, connected with the jet), weaker to higher frequencies. Thus, the HF-component of such spectra, measured by VLBI and by a single dish antenna, have to be practically the same. Such jets can exist in about 200 compact objects of our sample and seem to exist in majority or even all extragalactic compact objects.

Intraday variability (IDV) is a common phenomenon within blazars, and is seen in about 30 % of all sources in this class. Here we report on IDV observations carried out with the 100m telescope of the MPIfR, especially focusing on variations of the linear polarization.

The preliminary results of monitoring of simultaneous spectra of a sample of extragalactic sources are given. Eight sets of observations were done at the RATAN-600 radio telescope in 1995-1996 at six frequencies (0.96, 2.3, 3.9, 7.7, 11.2, and 22 GHz). The light curves as well as the variability parameters are given

Global VLBI snapshot observations at 1.6 GHz (5 EVN + 4 VLBA) of a sample of low-frequency variable (LFV) radio sources found using the Cambridge Low Frequency Synthesis Telescope (CLFST) are presented. Variability at 151 MHz is almost certainly due to propagation effects in our Galaxy (e.g., refractive interstellar scintillation). Theory indicates that only sources with a significant fraction of their low-frequency flux coming from components with angular sizes ≲ 30 mas will show such effects. This is confirmed by the VLBI images.

We report the results of a study of the long term and short term radio variability at 4.85 GHz of sources in the GB6 catalog.

Some comments on interstellar scintillation are presented.

VLBA observations of 32 compact sources within 30° ≤ ᶩ ≤ 75°, | b | < 3° are being used to test whether the galactic electron-density fluctuations contain a spiral component.

We present the first VLBA maps of Galactic H ɪ opacity towards the QSO 3C 138. The maps show significant opacity structure down to angular scales of 20 mas, which implies density structures in the cold neutral medium on physical scales of 10 AU or less

I present the results of a study of the global properties of combined complete samples of GPS and CSS sources. I discuss the constraints the results place on models for the evolution of these sources.

An optical study of CSS radio sources is presented.

We used our high-resolution radio images made with VLA of a large number of compact steep-spectrum (CSS) sources selected from well-defined samples of radio sources and the radio data of these samples to explore the evolution of CSSs with time. We suggest that the majority of CSSs are likely to be young sources advancing outwards through an asymmetric inhomogeneous environment to form the larger ones. We examine the symmetry parameters of both CSSs and larger sources and compare these with both analytical and numerical estimates of propagation of jets through an asymmetric environment. We also examine the consistency of CSSs with the unified scheme for radio galaxies and quasars.

A sample of gigahertz-peaked–spectrum (GPS) sources has been selected from the Westerbork Northern Sky Survey (WENSS) at flux densities one to two orders of magnitude lower than bright GPS sources studied until now. VLBI observations on our faint sample and other brighter samples provide evidence that GPS sources evolve in a self-similar way.

A few compact steep-spectrum sources (CSSs) have been observed with the VLBA at 8.4 GHz and MERLIN at 5 GHz to study the possible dynamical interaction between jets and the ambient media suggested by previous measurements of the rotation measures.

We are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing four frequencies (1.6, 4.8, 8.4 and 15 GHz) to get spectral-index diagnostics. In this paper, we present results on two galaxies, NGC 1068 and NGC 4151. NGC 4151 shows a curved radio jet on the sub-parsec scale, with the smallest scale structure misaligned by 55° from the jet on scales of parsecs to hundreds of parsecs. NGC 1068 contains several components in the inner tens of parsecs, with those components showing a variety of absorption and resolution effects.

The application of the VLBI technique to the study of gravitational lenses is described, and results from recent VLBI observations are reviewed.

We present results on the promising new gravitational lens system 1608+656.

We present λ7mm multi-epoch and polarization VLBA maps of the gravitational lens PKS 1830–211. The maps suggest that the radio structure of both images evolves rapidly. The offset between the polarized intensity and the total intensity may be used to constrain the magnification matrix.

PKS 1830–211 is the strongest known radio gravitational lens by almost an order of magnitude and has the potential to provide a measurement of H0, provided the lensing system can be parameterized. Attempts to identify optical counterparts, to measure redshifts, have so far proved unsuccessful and this has lead to radio and millimetre spectral line observations. We present our discovery of an absorption system at z = 0.19. A brief description is also made of our ATCA observations to measure the lensing time delay for this source.

We summarize results of a detailed imaging program of the molecular absorbing cloud at z = 0.88582 toward the “Einstein ring” radio source PKS 1830–211.

We present results from VLBI observations of the gravitational lens B1422+231. All the four images of this system have been detected and appear unresolved at 18cm. Images A and B show elongated structures at 6cm with 1 mas resolution. With a resolution of 0.75 mas at 2cm, three images are elongated with axial ratios of about 10:1 for A and B, and 2:1 for C.