No abstract

We present VLBI images of the compact high-luminosity radio galaxy 2352+495 that show symmetric structure on either side of a prominent central core. This contrasts strongly with the asymmetric nuclear structure exhibited by the great majority of powerful extragalactic sources. The outer structure of 2352 + 495 takes the form of. two "n;iini-lob~s" contain~ng hot spots! in this r~spect this compact radio galaxy resembles extende? radio galaxies, but its overa!l ~tze,-150 pc, ts-1000 times smaller. A reanalysis of existing data on th~ radio galaxy 0710+439 shows s1mtlar compact structure, and together these VLBI images confirm the ex1~tence of a ~lass of two-sided compact symmetric objects (CSOs). We show that, in contrast to nuclear rad10. sources m ot~er. powerful objects, the observed structure of CSOs is not dominated by relativistic beammg effects. It ts hkely that many objects previously classified as "compact doubles" will prove to be CSOs when mapped with VLBI with high dynamic range.

The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ∼10 in amplitude) flare in γ-rays towards the end of a 3-week pointing by CGRO, in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During the high state, extremely rapid γ-ray variability was seen, including an increase of a factor of 2.6 in ∼8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with RXTE, ASCA, ROSAT and IUE and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of ≃3) well correlated with the γ-ray flare without any lag larger than the temporal resolution of ∼1 day. The optical-UV light curves, which are not well sampled during the high energy flare, exhibit more modest variations (factor of ∼2) and a lower degree of correlation. The flux at millimetric wavelengths was near an historical maximum during the γ-ray flare peak and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The γ-rays vary by more than the square of the observed IR-optical Stanford, CA 94305

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. Aims. We obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. Methods. We present detailed kinematic analysis of the complete flux-density limited CJF survey. We computed 2D kinematic models based on the optimal model-fitting parameters of multi-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured and their reliability were performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, and core dominance and the resulting consequences is described. Results. With at least one velocity in each of the 237 sources, this sample is much larger than any available before, so it allows a meaningful statistical investigation of apparent motions and any possible correlations with other parameters in AGN jets. The main results to emerge are as follows: -In general motions are not consistent with a single uniform velocity applicable to all components along a jet. -We find a slight trend towards a positive outward acceleration and also adduce some evidence for greater acceleration in the innermost regions.-We find a lack of fast components at physical distances less than a few pc from the reference feature. -Only ∼4% of the components from galaxies and <2% of those from quasars undergo large bends i.e. within 15• of ±90• . -The distribution of radial velocities shows a broad distribution of velocities (apparent velocities up to 30 c). Fifteen percent of the best-sampled jet components exhibit low velocities that may need to be explained in a different manner to the fast motions. -Some negative superluminal motions are seen, and in 15 cases (6%) these are definitely significant. -We find a strong correlation between the 5 GHz luminosity and the apparent velocity.-The CJF galaxies, on average, show slower apparent jet-component velocities than the quasars. -The mean velocity in the VLBA 2 cm survey (Kellermann et al. 2004, ApJ, 609, 539) is substantially higher than in the CJF survey, the ratio could be roughly a factor of 1.5−2. This supports the observed trend toward increasing apparent velocity with increasing observing frequency. Conclusions. This AGN survey provides the basis for any statistical analysis of jet and jet-component properties.

We present the 5 GHz results from the first Caltech-Jodrell Bank (CJ l) VLBI survey. The 1.6 GHz maps were presented in two separate papers (Polatidis et al. 1995; Thakkar et al. 1995). These three papers complete the first stage of this program to map at both 1.6 and 5 GHz all objects accessible to Mark II VLBI in the complete sample of135 objects with 1.3 > SsGHz ~ 0.7 Jy, 0(1950) ~ 35°, and Jbl > 10°. The combination oftheCJl sample with the Pearson-Readhead (PR) sample provides a complete, flux density-limited sample of 200 objects with SsGHz ~ 0.7 Jy, o(1950) ~ 35°, and I bl > 10° for which all of the objects accessible to Mark II VLBI have been mapped at both 5 GHz (129 objects) and 1.6 GHz (132 objects). In addition to the 5 GHz VLBI maps, we present in this paper 5 GHz MERLIN observations of 20 objects and 1.4 GHz VLA observations of 92 objects in the combined CJl + PR sample. The VLA maps, together with Lband (1.3-1.7 GHz) maps available in the literature, provide a complete set of VLA maps for the combined CJl + PR sample. Finally, we present the radio spectra of the objects in the CJ l sample. The combined CJ l + PR VLBI surveys provide a sample which is large enough for a number of important astrophysical and cosmological studies. These will be presented in further papers in this series.