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Context. This is the second in a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-spectrum (hereafter CJF) sources and their analysis.

Context.We present the soft X-ray properties obtained in the ROSAT All-Sky survey and from pointed PSPC observations for the AGN in the complete flux-density limited Caltech-Jodrell Bank flat spectrum sample (hereafter CJF). CJF is a VLBI survey (VLBA observations at 5 GHz) of 293 AGN with detailed information on jet component motion.

Context.This is the first of a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-Spectrum (hereafter CJF) sources and their analysis.

9C J1503+4528 is a very young CSS radio galaxy with an age of order 104 years. This source is an ideal laboratory for the study of the intrinsic host galaxy/IGM properties, radio source interactions, evidence for young stellar populations and the radio source triggering mechanism. Here we present the results of a spectroscopic analysis of this source, considering each of these aspects of radio source physics. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and performance details are given for the Cosmic Background Imager (CBI), an interferometer array that is measuring the power spectrum of fluctuations in the cosmic microwave background radiation (CMBR) for multipoles in the range 400

Compact symmetric objects (CSOs) are young radio galaxies whose jet axes lie close to the plane of the sky, and whose appearance is therefore not dominated by relativistic beaming effects. The small linear sizes of CSOs make them valuable for studies of both the evolution of radio galaxies and testing unified schemes for active galactic nuclei (AGNs). A parsec-scale region of gas surrounding the central engine is predicted by both accretion and obscuration scenarios. Working surfaces, or "hot spots," and the radio jets of CSOs are close enough to the central engines that this circumnuclear gas can be seen in absorption.

The authors have measured the 10.8-GHz flux densities of 285 radio sources at 14 epochs between January 1979 and November 1982. For the subset of 258 objects constituting a complex flux-density-limited sample selected at 5 GHz, it is found that at least 45% vary within ten years. About nine-tenths of the steep spectrum (? ? -0.5) sources do not vary, whereas about two-thirds of the flat spectrum sources do. Quasars are much more likely to vary than either galaxies or empty field sources. Most objects from the S4 catalog identified with empty fields are galaxies beyond the plate limit.

A new four‐image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All‐Sky Survey. This system consists of four flat‐spectrum radio images that are also seen on a Hubble Space Telescope(HST) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HSTimages. The light distribution of the lensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of ∼1.33 for the lensed object; the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four‐image to two‐image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies.

In a small sample of extragalactic radio sources, curvature is found to be a common feature in bright radio components coincident with quasi-stellar objects. In 3C273 and 3C345 the curvature is smooth between the nuclear (<0.003″) and the outer (>1″) regions. This contrasts sharply with objects having comparatively faint central radio components, which are often well aligned with the extended features.

A core and a jet of length ∼ 1.7 pc have been found in the nucleus of NGC6251. The nuclear jet is aligned with both the 200-kpc jet and the outer lobes, which have a separation of ∼ 3 Mpc; the alignment persists over a range of scales \[gsims] 5 × 106:1. The observations provide strong evidence that energy and momentum are transferred continuously from the central core to the outer lobes by a beam.

VLBI observations of 3C147 reveal that its core is a low-frequency variable radio source which has brightened by a factor of 2 in 6 years. In combination with X-ray observations, this implies that bulk relativistic motion is taking place within the core, and leads to the prediction that 3C147 is a member of the class of superluminal radio sources.

Maps of the radio structure of 3C273 show directly that it expanded with an apparent velocity 10 times the speed of light from mid-1977 to at least mid-1980.

There are many situations in which it is possible to detect interference fringes, but with large systematic errors in amplitudes. A new method is described for mapping objects from such data. In principle this method is applicable to any system which can produce detectable fringes, and is not limited to radio frequencies.

We report the discovery of the most complex arcsec‐scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat‐spectrum core (quadruply imaged) and two compact ‘lobes’ symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HSTobservation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object is detected. A redshift of 0.755 has been measured for the lens galaxy.

The investigation of the nuclei of galaxies and quasars has been central to modern astronomy. The application of the technique of very-long-baseline interferometry (VLBI) to such sources has allowed the mapping of their angular radio brightness distributions and the analysing of their temporal changes. Many radio galaxies and quasars consist of a compact core, or centre of activity, and collimated jets of material ejected from the core with relativistic velocities1. Of particular interest are the brightness distributions and kinematics of the cores of such sources, because they may contain a supermassive object (SMO), possibly a black hole2(but see ref. 3 for an alternative view), with a mass of ∼109M ⊙(ref. 4) and a Schwarzschild radius of ∼3 x l014cm. We present here global VLBI observations of 11 radio sources at a wavelength of 7 mm, including a map of the brightness distribution of the active galactic nucleus in 3C84. This map has an angular resolution of 100 microarcseconds, unsurpassed in an image of a celestial object.

Between November 1974 and November 1975 the absolute intensity of H beta decreased by a factor of 1.8, while the strength of the forbidden line 4959 A of O III remained constant. The change was accompanied by a change in the nongalaxy component of the continuum light by a comparable factor. The evidence suggests that H alpha also changed by a similar amount. Over a twelve-year interval, the nongalaxy visual continuum changed by a substantially larger amount than H beta, suggesting that relative changes of the UV ionizing radiation and visual nongalaxy radiation are not proportional to each other on this time scale.

We propose a model of apparent superluminal expansion based on straightforward relativistic motion. The model gives a natural explanation of the ratio of radio-quiet to radio-loud quasars.

We have determined the radio structure of the quasar 3C147 from multi-baseline VLBI data at 609 MHz using both a conventional method and a technique which uses the ‘closure’ phase information to produce a good approximation to a synthesis map of the source. The structure is similar to the central part of M87, with a bright core and a linear ‘jet’ of projected length ∼ 1.5 kpc which is concentrated in bright ‘knots’.

Observations of radio sources at 81.5 MHz show that interstellar scattering is more important than some pulsar data suggest. Low frequency measurements also provide a new means for studying the distribution of ionized gas in the Galaxy.

In recent years the angular distribution of intensity of the compact cores of quasars and radio galaxies has been mapped in detail by very long baseline interferometry (VLBI) arrays1,2. These observations have shown that asymmetric radio structure is common in active nuclei3, and that a high proportion of the brightest sources exhibit superluminal motion4,5. The sources generally have an elongated structure, or jet, which dominates at long centimetre wavelengths, and a compact core at one end of the jet which dominates at short centimetre wavelengths. The association of the core components with the shortest wavelengths, and the most compact features, leads us to link core radiation with the unidentified central engines in these energetic systems. We report here the first detection of interference fringes by VLBI at a wavelength of 3.4 mm (89 GHz). The success of these observations demonstrates the feasibility of millimetre VLBI and opens this important wavelength range to mapping with a resolution of 10−4arc s. The compact radio source in the nucleus of 3C84 (NGC1275) was observed for a 9-h period on the 485-km (1.4 × 108λ) baseline between the Owens Valley Radio Observatory and the Hat Creek Observatory. These observations show that the structure is more compact at 89 GHz than at 22 GHz.

The superluminal quasar 3C345 has a curved, one-sided jet-like radio structure1,2. Ejected material has been observed travelling at apparent speeds of 13–17c (ref. 3). We report here new observations at 22 GHz which show that the most recently ejected component4is not moving radially away from the compact radio core, but along a trajectory which could be interpreted as either a curved path originating in the compact core, or a straight line, in which case the origin of ejection is not coincident with the compact radio core. The observations provide evidence of acceleration of this component.

Measurements of the angular sizes of radio source components in the range 0.1″–1.0″, using the technique of interplanetary scintillation, reveal an absence of small–diameter sources at the largest redshifts. The cosmological implications of this result are discussed.