We are undertaking a 1-baseline “cuts” VLBI survey of 461 flat spectrum radio sources selected from the Parkes Catalogue.

We continue to determine flux densities at 3mm, 2mm, and 1.3mm wavelength for selected extragalactic sources. Light-curves for some sources now cover nearly 12 years.

A sample of 15 bright AGN has been observed at 22 GHz with two epoch global VLBI observations. The sample consists of all sources in the complete 2 Jy catalogue of Valtaoja et al. (1992) previously unobserved at 22 GHz VLBI. We have begun to investigate how much structural information can be derived just from total flux density (TFD) monitoring and how to use total flux density observations to complement space VLBI observations. As an example we present Doppler boosting factors derived in four different methods.

VLBA observations of 130 quasars and AGN made at 15 GHz with submilliarcsecond resolution show a variety of structures, most of which appear linear.

The Very Long Baseline Array (VLBA) Calibrator Survey consists of snapshot observations at 2.7 and 8.4 GHz of nearly 2000 flat-spectrum extragalactic sources selected from the Jodrell Bank–VLA Astrometric Survey (JVAS). When complete, this survey will assist in defining the extragalactic radio frame in the northern sky by providing positions for these sources which will be accurate on the milliarcsecond scale. This survey is accessible on the WWW at http://magnolia.nrao.edu/vlba_calib/index.html.

8 GHz maps of 39 radiosources have been obtained with ≈ 0.5 mas resolution from geodetic VLBI-data. Structure variability has been investigated on ≈ monthly interval during the bursts of radio emission of two sources 0059+581 and 0202+149 in period from June 1994 to February 1996. Bright jet components in the sources show no steady outward motion, but may be some oscillations near stationary positions.

As part of our continuing study of parsec-scale magnetic fields in active galactic nuclei we have obtained deep polarization-sensitive images of the blazar 1055+018 with the VLBA at 5 GHz. These dramatic images reveal a magnetized layer of material on the outer surfaces of the jet, distinct from the bulk of the jet. This morphology suggests interaction of the jet with the surrounding medium, the resulting shear stretching the magnetic field lines in the direction of the flow. Further multi-frequency polarization-sensitive observations of 1055+018 offer the opportunity to study radio jet-ambient medium interactions in detail.

We present results of observations of two BL Lac objects, 0735+178 and 0723–008, with the European VLBI Network (EVN) at 1.7 GHz. These objects have a distorted morphology, characterized by a large misalignment between their inner and outer radio structures. Our EVN observations at intermediate resolution reveal the presence of a highly curved jet in 0735+178, providing evidence for continuity of the radio emission from milliarcsecond to arcsecond scales. No indication of connecting radio structure is found in the case of 0723–008.

The Rosat-Green Bank BL Lac sample consists of 119 objects and smoothly bridges the gap between the previously disparate subclasses of radio- and X-ray-selected objects. Further study of this sample should provide useful constraints to the unified scheme and help determine if modifications are necessary.

The polarization electric vectors in the VLBI jets of BL Lacertae objects are typically aligned with the jet structure. If the jet radio emission is optically thin synchrotron emission, this implies that the magnetic field is perpendicular to the jet, usually interpreted as a signature of shocks. The distribution of polarization position angles in the VLBI core components appears to be bimodal, with the polarization angles either aligned with or perpendicular to the jet direction. In order to study the origin of this characteristic polarization structure, we have made VLBI polarization observations of all 34 sources in the Kühr and Schmidt sample of BL Lacertae objects.

Observations with the University of Michigan 26-meter paraboloid at 4.8, 8.0, and 14.5 GHz have been used to test generic shock-based models of the emitting region of BL Lacertae. Large changes in the polarization position angle since 1980 are not consistent with a jet with a simple conical flow.

We have made polarization sensitive maps of BL Lac with the VLBA at 15, 22, and 43 GHz at seven epochs from 1995.42 to 1997.16. Three new superluminal components (S8, S9, and S10) have been identified, each having a unique signature in trajectory and polarization characteristics.

We present first results from a new sample of low radio luminosity flat spectrum radio galaxies.

New polarization-sensitive global VLBI and VLBA images of the BL Lacertae object 0716+714 at 6 cm (1991.4) and 3.6 cm/1.3 cm (1994.2) are presented. The source shows a compact, one-sided core–jet structure in structural position angle ~ 13°. The 3.6 cm total intensity image shows the jet beginning to curve toward the arcsecond-scale structure, which lies in position angle ~ −45°. Comparison with previously published data suggests that the apparent velocity of a 6 cm jet component is > 1.09 ± 0.15c, if the red shift of 0716+714 is z > 0.3. Linear polarization from the VLBI core was detected at all three frequencies; in addition, polarization from the innermost jet component was detected at 1.3 cm. This compact jet polarization appears to be quite high, ~ 50%, and to be aligned with the jet direction, which can be understood if it is a transverse shock. The VLBI core polarization at our earlier epoch was perpendicular to the VLBI jet direction, but had rotated to align with the jet direction by the later epoch, about a year later. This rotation may indicate the imminent birth of a new VLBI component (shock).

We have been monitoring gamma-ray blazars with the NRAO VLBA at 22 and 43 GHz since late 1993. We present results on three sources: AO 0235+164, 1633+382 (4C 38.41), and 2230+114 (CTA 102).

Preliminary results on the parsec-scale polarization properties at 15 GHz of 3 GHz-peaked-spectrum radio sources are presented.

PKS 1934–638 is an archetypal GPS source, peaking at 1.4 GHz and exhibits almost no flux density variability. VLBI images at frequencies of .843, 2.3, 4.8, & 8.4 were made with the southern hemisphere VLBI array and they reveal that the source is a 42 mas compact double. There is no detectable change in separation over the last 20 years, yielding an upper limit of ~ 0.03c ± 0.2c on any expansion velocity. The spectral shapes of the two components are remarkably similar, despite indications of finer structure on longer baselines. Magnetic field calculations indicate fields of a few mGauss and the results are consistent with equipartition.

Using new high resolution VLA and VLBA data and existing MERLIN data of 3C 67 and 3C 190, we find both sources have a complex spectral structure similar to larger Fanaroff-Riley type II sources. Our analysis of 3C 190 predicts either an unusually steep injection index of −0.8 and a young age, or a superposition of different age spectral components.

We discuss our VLBA observations at 5 and 2.7 GHz and our MERLIN observations at 1.6 and 5 GHz. A MERLIN+VLBA image provided good starting model for self-calibration and we obtained an unprecedent image of the bent jet of 3C 216. Our observations suggest the detection of strong polarization position angle variation across the observing band. If this is due to Faraday rotation then 3C216 may have a four-figure observed rotation measure, which is unlikely to be due to errors in the polarization position angle calibration.

We analyze polarization observations of 3C 147 at milliarcsecond scale which we have made with the VLBA at L, S, and C band and with the MERLIN array at K band. Several constraints placed by the observations on the physical conditions of the magnetoionic gas which produces the Faraday rotation are briefly discussed. Our data show that the Faraday rotation increases towards the VLBI core component with a maximum observed value of RM~ 4600±80 rad m−2. Such a value does not support the inclusion of 3C 147 as a source with exceedingly-high faraday rotation (SEFR), as suggested from published low-resolution observations.