The effect of the superluminal motion of 3C273b was observed on the fringe amplitudes obtained in VLBI experiments which have been conducted on the baselines between Japan and United States since 1984 under the Crustal Dynamics Project. The speed was 0.7 mas/year and the direction was −83 degrees in the position angle. It was also confirmed as the apparent right ascention shift of the source.

We review the information available on some bulk properties of the non-thermal emission regions in Active Galactic Nuclei, such as streaming motions, nature of composing particles, brightness temperature in the proper frame. Most of the information concerns the compact radio emission at relatively large distances from the center, whereas most of the action is thought to occur in the innermost regions which are observed at higher frequencies. We investigate whether these bulk properties can be understood within a general scheme for energy transport and particle acceleration around a magnetized rotating body.

Models of the small-scale structures in radio sources are limited by the resolution, dynamic range, and sensitivity of the observations upon which they are based. However, evidence from variability, brightness, and proper motion observations strongly support the contention that these objects involve directed outflow or ejection of material at relativistic speeds. The evidence for relativistic motion will be discussed, and a variety of models involving both bulk and pattern motion will be analyzed in terms of spatial and temporal characteristics which may distinguish between models. The possibilities and hazards of generalizing nonrelativistic jet models to the relativistic case will also be briefly discussed, especially regarding possible observational signatures of magnetized versus unmagnetized jets.

We have conducted a systematic study of the milliarcsecond structure of a complete, flux-density limited sample of strong radio sources selected at 5 GHz. We have made 5 GHz maps at two epochs of the 45 compact sources in the sample, and third-epoch observations are in progress. Our intention was to explore the full range of morphologies exhibited by compact radio sources, to search for new superluminal sources, and to determine how widespread such phenomena as parsec-scale jets, alignment of parsec-scale and kiloparsec-scale jets, and superluminal motion are. In addition, we hoped to use this well-defined sample for statistical tests of the beaming theories.

As part of a multi-epoch and multi-wavelength study of the physics of core dominated radio sources we have investigated the occurrence of apparent superluminal motion and other indications for bulk relativistic motion (b.r.m) in a statistically complete, flux density limited (S5GHz ≥ 1Jy) sample of 13 objects with flat radio spectra These sources come from the S5-survey (Kühr et al., 1981) and are optically identified as 7 quasars and 6 BL-Lac objects. They have been observed over a wide range of frequencies, from radio through X-rays (s. Eckart et al., 1986 and references therein). Radiomaps have been obtained at frequencies from 327 MHz to 22.2 GHz with resolutions from arcseconds to 0.2 mas, using the VLA, MERLIN and telescopes of the US- and European-VLBI networks. A recent status report on the VLBI-observations is given by Witzel (1987). In this paper we summarize the results on the direct evidence for b.r.m. in this sample as derived from repeated VLBI-observations at 5 GHz, as well as supporting evidence from SSC-calculations and flux density variability of the 5GHz VLBI core components (Table 1).

The evolution of compact double radio sources is discussed using a model due to Carvahlo (1985). We suggest that for doubles associated with active galaxies, there is a plausible evolutionary sequence from compact doubles to steep-spectrum compact sources to extended (D1) doubles.

We present the first results of a statistical study of the milliarcsec structure in a complete sample of radio galaxies. We have selected from the B2 and 3CR samples of galaxies the sources which present, at the VLA or WSRT angular resolution, an unresolved core with a flux density at 5 GHz Sc ≥ 100 mJy. The total sample consists of 30 radio galaxies, 17 from the B2 and 13 from the 3CR catalog. This complete sample covers a range of total radio power at 408 MHz log P = 23.5 – 26.5 W/Hz (low-intermediate luminosity). The radio structure of these sources on the arcsec-arcmin scale is well known, thanks to good dynamic range VLA and/or WSRT maps; a large variety of structures is present in the sample, from classical doubles to head-tail sources; flat, inverted and steep spectrum cores are also present.

We are investigating complete samples of southern hemisphere flat spectrum extra-galactic radio sources drawn from the Parkes 2.7 GHz Survey (see Bolton et al. 1979 and references therein). These samples are being used for a variety of investigations, including a determination of the space distribution and luminosity function of radio QSOs, their radio size distribution, as well as the structures of the individual sources. Accurate positions are being determined, as well, in order to establish an extra-galactic position reference frame in the southern hemisphere.

We have examined a relativistic beaming model using a VLBI survey by Preston et al. (1985). Our statistical study of a ratio R of the flux density for the beamed compact core to that for unbeamed components of a source shows Lorentz factor γ to be ≅ 6 and RT (R at transverse alignment) to be ≅ 10−2 for a sample of 222 QSO's. In addition, we find that a sample of 60 radio galaxies show the beaming effect with γ ≅ 4. It should be emphasized here that the beaming effect strongly affects the source counts (Log N - Log S) especially at high frequencies.

Following the success of a simple shock model for outbursts in BL Lacertae and 3C 279 (see Aller, Aller & Hughes, this meeting) we have constructed computer codes to study in detail the radiation from shocked, relativistic jets. These codes compute the transfer of synchrotron radiation, accounting for polarized emission and absorption, rotation, and mode conversion for a turbulent collimated flow with one or more shocks propagating parallel to the jet axis. We present results for a flow that evolves adiabatically, with the turbulence represented by a random component to the magnetic field within each computational cell, and with the shocks prescribed analytically following Königl (Phys. Fluids, 23, 1083, 1980). From the evolution of the total and polarized fluxes as a function of frequency, and from the corresponding projection of the source structure on the plane of the sky, we see that this type of model

1. a. is capable o f explaining the variability of compact radio sources - see Aller, Aller & Hughes, this meeting,

2. b. highlights the care needed when interpreting VLBI maps, in that

   1. i) the component separations are frequency dependent (see Fig. 1)

   2. ii) the ‘core’ is not always the brightest component (see Fig. 1)

   3. iii) the Doppler boosting factor of the shocked flow is not directly related to the Lorentz factor derived from the apparent superluminal motion of a component

   4. iv) a multiplicity of components can give rise to both apparent contractions and accelerations,

3. c. clearly shows the link between time variability of compact sources and evolving VLBI structure, and suggests that both may be understood in terms of weak shocks that tap a small fraction of a jet's flow energy,

4. d. enables us to probe the physical conditions of the flow and the ambient material.

We have analyzed the cm-wavelength flux and polarization observations of four active objects (3C 279, OT 081, BL Lacertae, and 3C 446) for which the data exhibit signatures of shocks. Common characteristics of these sources are: high degrees of polarization, large changes in the polarized flux during outbursts; and stable position angles of the electric vector over long periods.

The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (active nuclei or knots in jets) is considered under the assumption that particle acceleration takes place in shockwaves. Energy losses due to synchrotron emission and Compton interactions set upper limits to both electron and proton energies. In this case the upstream disturbance of the flow is dominated by the most energetic protons which are postulated, by analogy with the solar wind, to excite a turbulent wave spectrum of Kolmogorov type in this region. We predict for near relativistic flows a spectral cutoff near 3 1014 Hz independent of magnetic field. The observation of a sharp spectral cutoff near 3 1014 Hz is thus independent evidence for near–relativistic flows in jets.

The relativistic dispersion relation describing the spatial growth of a helical perturbation to a relativistic supersonic jet is applied to observations of the nonlinear superluminal acceleration of component C4 along the inner jet in 3C345.

Dual relativistic effects in compact radio sources are discussed, and as an illustrative example we try to show that the observed features of the knot C4 in 3C345 (superluminal motion, superluminal expansion, apparent diameter and flux variation etc.) can be interpreted simultaneously.

We have mapped the nearby (z=0.018), active galaxy NGC 1275 (3C84) at 6 different epochs from 1981 to 1986 at 1.3 cm (22.3 GHz) with a global VLBI array of seven telescopes. We find a long-lived knot of emission separating from the brightest radio component with a projected velocity = 0.4 6±0.12 h−1 c. This knot moves through diffuse emission that also moves away from the main component with a slower projected velocity of 0.33±0.12 h−1 c. We show that the knot and diffuse emission result from two separate events that occurred around 1959 and 1968.

We have made λ 3mm VLBI observations of 3C84 at 6 epochs between 1981 and 1987, using 6m antennas at the Hat Creek Radio Astronomy Observatory (HCRK), 10m antennas at the Owens Valley Radio Observatory (OVRO), the 12m Kitt Peak telescope (KTPK), and the 14m telescope at the Five College Radio Astronomy Observatory (QBBN). Model fitting suggests a core-halo structure, which we associate with the active nucleus of NGC 1275. The unresolved core, which is smaller than 0.1 pc (0.2 mas; z=0.018; H =50 km s−1 Mpc−1) shows a slow decay corresponding to the decrease in total flux density since the flare in 1980. In 1985 we resolved the core component on a transcontinental baseline (109λ) into a compact nucleus, < 0.1 mas, and a “jet” extended at a position angle 205° and unresolved in width, < 0.1 mas. There is also evidence for a compact emission region located 10 mas from the nucleus at a position angle 170°. This structure corresponds closely with that observed at the same epoch in VLBI maps at 22 GHz.

We have observed the core of the steep spectrum compact quasar 3C147 at a wavelength of 6 cm with an intercontinental VLBI array. The three observing epochs cover a period from 1981.25 to 1984.8. The core of 3C147 exhibits a complex, nonlinear, and asymmetric structure. It shows structural variability as well as variations of individual components. The observed changes in separation corespond to an apparent velocity of 2.6 ±1.0 c (H0 = 50 km s−1 Mpc−1, q0 = 0.5). In addition a map from the 3-station observation in 1978 is presented.

Observations of short term flux variations provide one of the few means of determining the smallest scale sizes in compact radio sources. The fastest variations are generally found in BL Lac-type objects, OJ287 being one of the best studied. In 1985 Valtaoja et al. (Nature 314, 148) found evidence for variations at a level of (typically) a few % with a period of in OJ287 at frequencies of 22 and 37 GHz. [Such periodic variability was, however, not detected at 5 GHz during one of their observations by Dreher et al. (Nature 320, 239, 1986)].

We have defined a complete sample of double-lobed 3CR quasars with minimal orientation bias. Properties of these objects on the >kpc scale are consistent with the simple beaming model for their nuclei. VLBI maps of six nuclei reveal “core-jet” structures. Both nuclei mapped at multiple epochs are modestly superluminal (3C245, 3.1c; 3C263, 1.3c; H0=100 km/s/Mpc, q0=0.5). The distribution of apparent velocities in this sample will provide a stringent test of beaming.

On 1983 May 10–11 we undertook simultaneous λ3.6 and λ13 cm Mark III VLBI observations of the quasars 1038+528 A,B. Our experimental conditions (i.e., synthesized band, uv-coverage, etc.) were almost identical to those we used on 1981 March 17–18. Thus, we could make a direct comparison of the results from both epochs.