The quasar population as a whole covers a wide range of continuum properties; sufficient to cause a marked difference in the physical conditions of the gas in the nuclear region of a quasar. In this paper we will discuss our results on 3C351, an X-ray “quiet” quasar; and 3C212, a “red” quasar. We identify the “warm absorber” observed in the ROSAT observations of 3C351 to be the UV absorber observed by HST.

We describe an optical, spectroscopic survey of the nuclei of the 500 brightest galaxies in the northern sky. The primary goal is to search for low-luminosity active galactic nuclei (LLAGNs) in the centers of nearby galaxies. The results of this survey will have many astrophysical applications, including quantifying the faint end of the local AGN luminosity function and estimating the contribution of LLAGNs to the X-ray background. We summarize the statistical properties of the survey, describe our methods of analysis, and present some preliminary results based on ∼ 60% of the sample.

Hierarchical cosmogonies can consistently explain the evolution of the quasar population if quasars are short-lived and supermassive black holes form fast in the newly-formed nuclei of dark-matter haloes. Here we investigate the relevant physical processes and show that such a fast formation is plausible. The angular-momentum and the gas-supply problem for the formation/feeding of a supermassive black hole are strongly alleviated compared to a scenario in which gas is transported to the centre by tidal interaction of ready-assembled galaxies. The baryonic component of the newly-formed nucleus will cool catastrophically and settle into a self-gravitating angular momentum-supported disc of radius ∼ 100 pc. Gravitational instabilities and/or supernovae-induced turbulence will transport the gas further to the centre within less than 108 yr. In nuclei of very massive dark matter haloes with sufficiently deep potential well to retain the gas against feedback processes from massive stars and supernovae, concentration of a major fraction of the gas component of the nucleus within the central 1 pc and subsequent formation of a black hole seem unavoidable. A coeval short phase of efficient star formation could explain the observed high metallicities of quasars.

Nuclear jets containing relativistic “hot” particles close to the central engine cool dramatically by producing high energy radiation. The radiative dissipation is similar to the famous Compton drag acting upon “cold” thermal particles in a relativistic bulk flow. Highly relativistic protons induce anisotropic showers raining electromagnetic power down onto the putative accretion disk. Thus, the radiative signature of hot hadronic jets is x-ray irradiation of cold thermal matter. The synchrotron radio emission of the accelerated electrons is self-absorbed due to the strong magnetic fields close to the magnetic nozzle.

HST Planetary Camera narrow band emission-line and continuum images are used to study the nuclear region of NGC 4151 at the highest possible spatial resolution. The [O III] λ5007 image reveals a striking biconical structure with a projected opening angle of 75° ±10°, and whose apex coincides with the bright, unresolved central source. The projected axis is oriented along PA 60°/240° ± 5°, and is aligned with the extension of the nuclear VLBI radio source. Analysis of the geometry of the narrow-line region places our line of sight well outside the ionization cones, and yet we see nearly unobscured optical and near-UV continuum and broad lines. In addition, material with significantly different column densities is required to explain the numerous optical and UV absorption lines and the soft X-ray absorption. We conclude from these data that the simplest version of the obscuring torus unification model is inconsistent with the observations and some modifications are required. We discuss some alternative collimation mechanisms that are compatible with our observations.

The standard big bang cosmology has the universe created out of a primeval explosion that not only created matter and radiation but also spacetime itself. The big bang event itself cannot be discussed within the framework of a physical theory but the events following it are in principle considered within the scope of science. The recent developments on the frontier between particle physics and cosmology highlight the attempts to chart the history of the very early universe.

The Unified Model states that the classification of individual AGN is a function of orientation, and that orientation effects are key to understanding the different classes. In its most extreme form, it states that every AGN has a featureless continuum (FC) source and a broad line region (BLR), both enclosed in an opaque torus. The torus is perpendicular to the associated radio structure axis. For the powerful radio sources (in Elliptical galaxy hosts), the jets undergo bulk relativistic motion, giving rise to phenomena such as superluminal motion associated with the blazar class. All strong radio sources have diffuse double radio lobes, although in the blazars one is sometimes seen projected onto the other. To take this to the extreme, we can suppose that all opaque tori are made of dust and have the same opening angle and that the radio jets are all narrow and have the same bulk-motion Γ factor.

There are now well established classes of X-ray emitting galaxies, which exhibit characteristic ranges of luminosity, for example Green et al. (1992). The ROSAT all sky survey, has detected a relatively small number of galaxies whose overall properties do not appear consistent with any of these classes. We discuss whether these X-ray luminous galaxies (XLGs) are the extreme end of the luminosity range of starburst galaxies, or whether they represent a new X-ray class of AGN.

We report results of an international UV – X-ray campaign in 1990–1992 involving the IUE, Rosat and Ginga satellites to observe E1615+061, a Seyfert 1 galaxy with peculiar spectral and intensity behaviour over the last 20 years. The source has been found to be stable in its medium state during the observations. The Ginga (1–20 keV) spectrum of E1615+061 is adequately represented by a simple power law with a photon index α = 1.8 ± 0.1. However, α ∼ 2, as expected for the intrinsic power law component in a reflection model, cannot be ruled out statistically. The Rosat PSPC (0.1–2 keV) spectra collected during the All Sky Survey and the AO-1 phase can be well-described by a simple power law (α = 2.2 ± 0.1) with cold absorber (NH = 3.5 ± 0.3 · 10λ20 H/cmλ2). Both the photon index being significantly different than that obtained from the Ginga spectrum and the column density being smaller than the galactic column (NH ∼ 4.2 · 10λ20 H/cmλ2) give an indication of a soft excess over and above the hard component seen in the Ginga spectrum. E1615+061 has been observed with IUE in 1990 and in 1992. The source was stable and the colour excess E(B-V) derived from the data = 0.1 is in good agreement with that expected from the galactic absorption.

To parameterise the soft excess we fitted the Rosat data with a two-component model consisting of a power law, and a blackbody or thermal bremsstrahlung, with a single galactic absorption term. The column density and the slope of the power law were kept constant. The blackbody temperature was 80 ± 6 eV and 63 ± 12 eV for photon index equal to 1.8 and 2.0, respectively, whereas the bremsstrahlung temperature was 220 ± 40 eV and 115 ± 30 eV for the two cases.

An attempt to model the soft excess seen in the Rosat PSPC spectrum has been made assuming that the soft excess is the high energy tail of a disc spectrum which peaks in the UV part of the spectrum. Additionally it was assumed that there is a hard component contributing to the spectrum from UV to X-rays with parameters as described by the Ginga spectrum. The best fit parameters: the mass of the central source and the mass accretion rate were around 5 ± 1 · 10λ6 M⊙ and 0.2 ± 0.04 M⊙/yr, respectively.

Our modelling shows that the soft X-ray excess can be described (χredλ2 < 1.2) as the high energy tail of an accretion disk spectrum if the intrinsic power law is quite steep (α = 2). The main contribution to the residuals in the Rosat PSPC range comes from 0.3–0.6 keV, with a tendency for these residuals to increase when the slope gets flatter. The accretion luminosity is ∼ 6.5 · 10λ44 erg/s for the best fit parameters, i.e. about the Eddington luminosity.

The optical through X-ray spectra of 3 QSOs between z = 1.32 and 3.53 show these objects to be very similar to low z AGN.

We present ground-based data of the BL Lac object PKS 2155-305 obtained during a large international campaign spanning the electro–magnetic spectrum from the radio waves to X-rays in November 1991. For the complete description of the observations and data analysis we refer to the paper by Courvoisier et al. 1993, and references therein. The ground-based data include radio, infrared JHKL and UBVRI fluxes as well as optical and near IR polarimetry.

The broad-band optical and near IR data from U to I exhibit the same behaviour in all bands: the flux nearly doubled over the well-covered period of 23 days. The cross-correlation function does not reveal any significant changes in the light-curves. Though significant variations in 24 hours have been recorded, the cumulated Fourier power spectrum drops to the noise level for periods shorter than 2.5 days. The spectral index remained constant.

The polarised flux varied by a larger factor than the total flux and did not follow the same pattern. The degree of polarisation and polarisation angle are nearly independent of the wavelength and are strongly correlated in all filters.

In the radio domain the spectral index increased from −0.1 on November 5 to +0.02 on 25-th.

The absence of the lag between the optical and infrared bands and the polarisation variations are consistent with a model in which the variability is caused by micro-lensing of the source (Stickel, Fried and Kühr 1988). One would, however, expect in this model that the variation in the polarisation and the total flux are tightly correlated contrary to what is observed.

The constant shape of the continuum spectral energy suggests that only the number of electrons whose emission is beamed towards the observer changes, rather than the arrival of fresh electrons that are being accelerated.

The variability of the polarisation may be explained by changes in the geometry of the magnetic field (dominant direction). This is consistent with the observed variations of the polarisation angle.

We analyse multifrequency quasi-simultaneous observations of AGNs with the Inverse Synchrotron Transform (IST) method described in Salas et al. (1993) and in Paper I (this conference).

The observational spectral energy distribution of blazars and OVV quasars used as applications of the IST method were obtained from multifrequency quasi-simultaneous observations of Landau et al. (1986) and Brown et al. (1989). The application of the method requires good spectral coverage, since the presence of gaps larger than ≈ 0.75dex can introduce ficticious peaks. We present the analysis for: 1749+096, 0735+178, 1308+326, 3C273, 3C345, 3C279, OJ287, OJ049, 3C216, 4C39.25.

The observed spectra are transformed to the source rest frame, the inverse transform is calculated over the whole spectrum to derive the electron energy spectra, which gives the amount of energy emitted in each characteristic frequency. Our results show that the electron energy spectra, Ψ(vc), of blazars and OVV quasars consists mainly of 4 or 5 well defined peaks superimposed on a down curved continuum. This indicates that the source radiates mainly around certain values of the electron's critical frequency (or energy, since vc ∞ B E2). These peaks are consistent with injection of fresh relativistic particles, occuring in pulses of quasi-monoenergetic groups.

The separation between successive peaks (Δp) is ≈ 1.2 dex in critical frequency, and is characteristic for each object. The peaks in the radio region contain approximately the same number of electrons, consistent with evolution given by the continuity equation for constant B. While in the OIR region, the energy radiated increases towards lower frequencies.

A comparison of Δp with Lbol and Lradio, and jet parameters such as, jet velocity and B1pc (inferred from the relativistic jet models of Blandford and Königl 1979) given by Cruz-Gonzàlez and Carrillo (1991), shows that Δp increases with jet velocity, stronger B fields imply smaller Δp, and that it is not correlated with Lbol, but is apparently correlated with Lradio.

The Inverse Synchrotron Transform method applied in this paper is a powerful tool in the analysis of spectral energy distributions of AGNs.

We obtained simultaneous optical spectrophotometry (4000-8000 Å) and near-IR photometry (JHKL) for 34 blazars, with repeated observations for 21 of them. All the data were taken at ESO and cover a period of 3 years with a typical time interval of 6 months. The observations were corrected for interstellar extinction and analyzed using a uniform procedure. This allows to form a large and homogeneous data set of optical-near-IR measurements of blazars emission.

We have studied the first extreme ultraviolet spectroscopic data and a high accuracy light curve for the BL Lac object PKS 2155–304 observed with the Extreme Ultraviolet Explorer (EUVE) on July 21–22, 1992. This target was observed with the Deep Survey Spectrometer telescope for approximateley 30,000 sec during the in-orbit-calibration phase of the mission, allowing to obtain simultaneous image and spectrum.

We present SEDs for Cen A, NGC 4151, 3C273 and 3C279 with new results from the CGRO. The spectra cover 16 orders of magnitude in v, radio to γ-ray, over 20 years of observations. These 4 galaxies represent a Seyfert, a FSRG and 2 blazars. The γ-ray data indicate two classes of AGN. At γ-ray energies Type 1 Seyferts and radio galaxies have quantitatively different properties from blazars.

Hughes etal. (1993) have made submillimetre continuum observations of 10 IRAS selected radio-quiet quasars (RQQs). Three RQQs, I Zw 1, Mrk1014 and Mrk376, have been detected at 800 and 450μm using the 3He bolometer UKT14 on t he 15-m James Clerk Maxwell telescope. These submillimetre data, together with existing 1.3 mm observations (Chini etal. 1989) demonstrate that the measured submillimetre spectral indices, 〈αsm〉 = 3.8 ± 0.5, significantly exceed the critical theoretical limit of αsm = 2.5 predicted for the self-absorption of synchrotron emission. This result is independent of any contributions to the 100μm IRAS fluxes from cirrus emission in the host galaxies, extended circumnucl ear starformation and FIR emission from companion or confusing sources. All current non-thermal models (de Kool & Begelman 1989, Schlickeiser etal. 1991) are rejected in favour of the alternative explanation that the FIR luminosity is dominated by thermal emission from warm (45–60 K) dust grains. The submillimetre optical depth and source-size for the thermal emission cannot yet be constrained by these data and, as a result, no discrimination can be made between dust heated by an extended (> 1 kpc) starburst region or a central compact luminosity source. However ground-based imaging observations at mid-IR wavelengths and FIR photometry (60–200μm) with the KAO are currently in progress specifically to address this problem. The high gas masses (> 1010M⊙) in RQQs inferred from the submillimetre continuum observations are in agreement with the H2 masses determined from CO measurements. Alternatively the results show that the MH2/Mdust ratio measured in RQQs (∼ 370 ± 150) is consistent with that measured in spiral galaxies and ultra-luminous IRAS galaxies.

The first extreme ultraviolet spectrum of NGC 5548 obtained by EUVE is presented.

Preliminary spectral results are presented for the 100 objects, selected from a VLBI-servey at 6–7 wave lengths of 31 cm, 13 cm, 8.2 cm, 7.6 cm, 3.9 cm, 2.7 cm, and, for the declinations greater than +13 degrees, at 1.38 cm. The most of presented spectra may be resulted by the emission of a halo-jet structure of AGNs.

From June 15 to 28, 1991 the Compton Gamma-Ray Observatory (CGRO) observed the radio-loud quasar 3C 273. All four CGRO instruments detected radiation from this quasar in their relevant energy range (from 20 keV to 5 GeV). Simultaneous and quasi-simultaneous observations (spanning the time period May 27 – July 25, 1991) by instruments sensitive at other wavelengths have also been obtained. The data from all these observations spanning the frequency range from ∼ 109 Hz to ∼ 1026 Hz were collected and analysed. The resulting energy-density spectrum is shown in the figure below. It shows two maxima, one in the UV, another one at low-energy γ-rays which have nearly the same strength (the corresponding luminosities per decade of frequency for H0 = 60(km/s)/Mpc are 3.2·1046 erg/s and 2.7·1046 erg/s, respectively). A break of the spectrum at low-energy γ-rays is evident. From a detailed analysis a break energy of (2±1.5) MeV could be derived corresponding to a frequency of (4.8±3.6)·1020 Hz. The observed spectral break between X- and γ-rays is ∼ 0.8, much higher than the value of 0.5 predicted by some models. A more detailed paper on this topic is in preparation (Lichti et al.).

We have monitored a sample of 17 blazars at 375, 270, 230 and 150 GHz with the James Clerk Maxwell Telescope (JCMT). We also have 230, 150, 90 GHz data from IRAM and SEST, and 37, 22 GHz from Metsähovi Radio Research Station, Finland. The data shows a range of flaring time-scales, from months for e.g. 0851+202 to years in the case of e.g. 1641+399. Superimposed shorter time-scale variability (‘flickering’ behaviour) is seen in many sources from our sample. We make no conclusive statements on whether BL Lacs as a class are preferentially variable on shorter time-scales. All sources show variability on many time-scales regardless of classification.