Simultaneous (5672 Å and 3400–3900 Å)) optical continuum photometric observations of the Seyfert galaxy NGC4151, were carried out within ≤4 week periods, down to a time resolution of < 1hr. A new active phase (1990) is detected with onset and slope captured in 1989. Implications of the variability record from 1983, to 1990 (Fig-1), are discussed.

The International AGN Watch collaboration undertook an intensive monitoring campaign of the bright Seyfert 1 galaxy NGC 3783 between December 1991 and August 1992, in order to study the variations of the continuum and broad emission lines. Spectroscopic and photometric observations took place at several ground-based observatories and formed the optical/IR counterpart to the UV observations conducted with the IUE (Reichert et al. 1993).

We report on the results of a UV-Optical spectral monitoring of the bright Seyfert 1 galactic nuclei Mkn 335. This campaign began in June, 1989, and ended in June, 1991. Ultraviolet spectra of fourteen epochs at nearly uniform sampling of 30-day intervals, except when the object was inaccessible from the IUE satellite, have been obtained, of which twelve were coordinated with quasi-simultaneous ground-based optical observations made at Lick Observatory.

We have collected all the observations available to us of blazar OJ 287. Here we will present preliminary results from our investigation of these data. The photometric light curves show large outbursts occuring (quasi)simultaneously in all frequences. The largest outbursts occured during 1972 and 1983. The B-band light curve can be extended to the year 1894. This being the longest available observational data set of all blazars. Polarization light curves in optical show random variations in all timescales. In the radio bands the polarization observations show well defined structure in the light curves. Light curves and simple correlation analysis based on the light curves on different frequences will be presented.

The monitoring of extragalactic sources with the Metsähovi radio telescope started in 1980. Since then we have made more than 21000 observations at 12, 22, 37, 77 and 87 GHz. Currently we have 84 sources in our sample which should be observed once a month at 22 and 37 GHz. The sample is limited to declinations above −10 degrees. In most cases our sampling is dense enough to cover all the outbursts at these two frequencies, because our earlier observations have shown the timescales of a typical outburst at 22 and 37 GHz to be from 0.3 to several years.

We have been searching for correlated optical and radio variability in large temporal data sets of 22 extragalactic radio sources. The optical data were obtained with the 76-cm reflector at the Rosemary Hill Observatory in Florida, USA. The radio data were obtained at two different sites: 22, 37 and some of the 90 GHz data at the Metsähovi Radio Research Station, Finland, and 90 and 230 GHz data at the Swedish-ESO Submillimetre Telescope (SEST) on La Silla, Chile. Because the SEST data unfortunately reaches only back to 1988, the 90 and 230 GHz data were complemented by the IRAM data from Steppe et al. (A&AS 75, 1988 and A&AS 96, 1992).

We report some results of a new analysis (Trèvese et al. 1993, ApJ (submitted) (T93)) of the variability of the faint QSO sample of SA57 (Koo, Kron and Cudworth, 1986, PASP, 98, 285), concerning the intrinsic time scales of variability and the dependence of the amplitude of variability on absolute magnitude and redshift. Prime focus plates of SA57 have been obtained with the Mayall 4-m telescope at the Kitt Peak National Observatory since 1974. The present analysis is based on 14 BJ plates spanning 15 years at 11 independent epochs. The digitization, object selection, image classification and photometry are described in Koo (1986, ApJ, 311, 651) and Trèvese et al. (1989, AJ, 98, 108 (T89)). The magnitude limit of the sample is BJ = 22.5 and stellar objects are selected with a threshold in image size. This criteria give a sample of 694 objects in the field, 34 of which are QSOs whose spectra have been measured with the Mayall 4-m telescope. The r.m.s. error in the BJ band is 0.05 mag at BJ Ã 22 mag. All but one of these QSOs appear to be variable according to T93.

The multifrequency spectra of Blazars 3C 279 and 3C 345 are presented and their implications for theoretical models are discussed. The spectra resulted from two separate but complimentary observational programs; one a serendipitous discovery by CGRO that extended the spectrum up to GEV energies, while the other a program designed to investigate the spectral variability of a Blazar during an outburst.

We have observed 11 radio quiet QSOs (RQQSOs) to see if they exhibit intranight variability in the optical. The detection of such microvariability would support models in which fluctuations on accretion disks are dominant, while if it is never present, models based on relativistic jets would be favored. Although several of these RQQSOs show hints of microvariability, we cannot claim to have discovered this phenomenon in this class of objects. Several of the comparison stars have clearly shown rapid variability.

We present the preliminary results of an 8-month monitoring campaign carried out on 6 AGN during the period December 1991 – July 1992. All but one of our targets showed continuum and/or line variability. The data were obtained using the 2D-Prutti + Cassegrain spectrograph at the CTIO 1.0-m telescope, and reduced following standard procedures. The slit width was 5″ and the nuclear spectra were extracted in a 10″ aperture. The wavelength coverage is 3500–7200Å, with 8Å resolution. The data were flux calibrated using standard stars and then normalized using the [O III] λ5007Å line flux for each object. NGC 6814: our spectra reveal that this object is still in a low state of activity and within the S/N ratio of our data, no variability was observed during this campaign. The stellar population is dominant in the nuclear spectrum and a synthesis using the star cluster library of Bica (1988) indicates a mainly old (∼ 86% of the continuum flux at 5870Å due to a population with age ≥ 10 Gyr), [Z/Z⊙] ≥ 0.3 stellar content, with an intrinsic reddening of E(B–V)=0.20. NGC 3227: using an off-nuclear spectrum corresponding to the two 5″×10″ regions 20.4″ E/W of the nucleus, we obtained also a mainly old (77% at 5870Å with age ≥ 10 Gyr), [Z/Z⊙]=0.3) synthetic stellar population, which contributes ∼ 43% of the nuclear light at 5600Å. The cross correlation of the 4245Å continuum and Hβ light curves results in a 18±3 -day lag. IC 4329A: our data show evidence of variability as a slow and constant increase in both continuum and lines fluxes, but no isolated event was detected. ESO141-G55: the light curves show small variations in the continuum, but no noticeable line variability. Akn 120 and Fairall 9: the data consists of two sets of spectra, separated by ∼ 6 months. Within each set little or no variability was detected, but strong line and continuum variations occurred between them.

The activity in the nuclei of bright galaxies could arise from a number of sources: they may contain compact variable radio sources, they may be strong IR/optical/X–ray continuum sources, or they may have strong emission lines. Usually but not always these properties go together as in radio loud quasars. However, there appears to exist a class of objects which resemble quasars in radio structure and brightness – have strong flat spectrum cores but appear fainter than would be suggested by their radio brightness – unidentified on sky surveys (Zensus & Porcas, 1985, in J. Dyson, ed, AGN). These are called ‘optically quiet quasars’ (OQQs).

Snapshot VLBI observations at 18 cm have been obtained with a global array at three epochs (1980.1, 1981.8, 1987.9) in order to investigate flux density and/or structural variations for a sample of 21 low frequency variable sources (Padrielli et al. 1987 Astron Astrophys. Suppl. Ser., 67, 63; Bondi et al. 1993 in preparation).

Observations suggest that the flow speeds in extragalactic radio jets are relativistic on parsec scales. This evidence includes rapid variability, brightness temperatures in excess of the inverse Compton limit and even the motion of individual features with apparent superluminal velocities. In contrast, FR–1 flow speeds appear to be non–relativistic on kiloparsec scales (the case is not clear for FR–2 sources); consequently, the possibility of jet deceleration has been explored.

Surprisingly few Seyfert galaxies have been mapped at near optical resolution in the 21–cm line of neutral atomic hydrogen, despite the fact that studies of the gaseous component hold out the possibility of identifying the cause of infall of gas to or outflow from the central region. We therefore decided to observe the Seyfert 2 galaxy NGC 1068 with the NRAO–Very Large Array. The spatial resolution of the final images is about 8 ″ or 700 parsec at a distance of 18 Mpc; the velocity resolution is 5.2 km s−1.

Geodetic VLBI observations of extragalactic radio sources –designed to measure earth orientation parameters– are performed regularly since more than 10 years now. In different campaigns about 20 Quasars and BL Lacs are being monitored at 2.3 and 8.4 GHz. The high duty-cycle of these observations (every month for IRIS-S) and the resulting enormous data base allow to study the milliarcsecond structures and their variations simultaneously at two frequencies on short timescales. Since the accuracy of baseline determination and measurement of earth rotation parameters has reached a limit where source structure contributions become significant, there is substantial interest to monitor and correct for the source structure “effects”. Therefore we perform a regular analysis of sources selected from IRIS-S (high north-south resolution and almost circular beam for low declination sources) and EUROPE (high sensitivity due to large telescopes) campaigns covering a maximum time base of 10 years (1983–1993). The (undesired) structure of the sources leads to an occasional updating of the source catalogue in order to have “pointlike” sources which are observed 10–15 times for three to seven minutes during 24 hours. Meanwhile about 50 sources have been observed in geodetic campaigns. The comparatively poor data quality requires careful calibration with a source whose structure is well–known from high dynamic range observations (e.g. the blazar 1803+784). The dynamic range of these maps is limited to 1:50. The merit of this database lies obviously in the monthly persecution of structural changes in extragalactic radio sources over at best 10 years time and the filling of the gaps between high dynamic range observations. Sources which are presently of particular interest to us, include 1803+784, 4C39.25, 0528+134, 3C454.3 and OJ287.

The GHz-Peaked-Spectrum (GPS) radio sources are galaxies and quasars with compact structures on scales of tens to hundreds of parsecs and spectrum peaking around 1 GHz. Phillips and Mutel (1982) suggested that the double GPS sources (also called compact doubles, CD) are an early stage of the evolution of the classical double sources of Fanaroff-Riley class II type. We have presented a model (Carvalho, 1985) in which we show that the properties of the CD sources are consistent with such a scenario. Their ages would be of the order of 104 yr.

GHz-Peaked Spectrum (GPS) radio sources are intrinsically small (< 1 kpc) and unbeamed objects. The galaxies considered here (0316+161, 0404+768, 0428+205, 1323+321, 1358+624, 1819+39, 1829+29) have been selected from the Peacock and Wall (1981) catalogue, and belong to a complete sample of Compact Steep-Spectrum (CSS) radio sources (Fanti et al., 1990). Their radio spectra show a turnover which could be explained in terms of synchrotron self-absorption. It occurs at frequencies ranging from about 100 MHz to 5 GHz and for this reason they do not appear in the 3CR catalogue.

The major contending scenarios capable of explaining various aspects of the Seyfert phenomenon in AGNs are (i) the Super-massive Black-Hole model and (ii) the Starburst model. Detailed optical emission-line and radio images of Seyfert nuclei, and their mutual correlations, provide important clues in evaluating the claims of each. Using the EVN at λ 18 cm, we have mapped four Seyfert galaxies, Mkn 1, 3, 231 and 463 at a resolution of ∼ 25 mas. The maps, and comparisons with images at other wavelengths, will be presented elsewhere (Ghosh et al. 1993, in preparation). Here, we present parameters derived from elliptical-Gaussian fits to all discernible components (Table 1).

The results are presented of a program to study the radio structure of radio galaxies, and to compare them with quasars. The samples are matched in redshift and luminosity in the redshift range 0.2 to 1.0, and mapped with the same VLA configuration. The quasar results have been published in earlier papers and the radio galaxy results are in press. We compare 100 quasars with 80 radio galaxies. The comparison shows the following radio galaxies differ from quasars in the following ways:

1. 1) The overall sizes are larger for radio galaxies by 2 to 3 times.

2. 2) There are few large bend angles in radio galaxies.

3. 3) The lobe length ratio distribution differs.

4. 4) The radio galaxies have no population of one-sided sources.

5. 5) The lobe flux ratio has less range in the radio galaxies.

6. 6) Radio galaxies have few core-dominated sources and many with no detectable core: few with comparable core and lobe flux.

7. 7) The most luminous sources are lobe-dominated and more powerful than the quasars. The most luminous quasars are unresolved cores.

Points 1,2,3 can be fit with a single ‘unified’ model which has a distribution of sizes and bend angles up to 25°, with small expansion velocities. The quasars are viewed within a cone angle of 50° and the radio galaxies outside the cone. However, the model does incorporate a source growth scenario and points 4 through 7 imply that there are instrinsic differences between the source types as well as orientation. We also discuss the limitations on beaming and bulk motions implied by the results.

Recently the 1.5 years flux observations of a quasar 0235+16 at 8 frequencies have been explained by the emission of a jet in a strong radial magnetic field of an AGN (in according with the Hedgehog model, suggested by N.S. Kardashev in 1969; see poster by Kovalev Y.Y. and Larionov G.M. to this Symposium).