Multiwavelength observations of the hard X-ray selected sources discovered by BeppoSAX, Chandra and XMM-Newton surveys have significantly improved our knowledge of the AGN population. The increasing number of X-ray obscured AGN so far discovered confirms the prediction of those AGN synthesis models for the X-ray background based on the Unified scheme. However, follow-up optical observations of hard X-ray selected sources indicate that their optical properties are quite varied and the simple relations between optical and X-ray absorption are by no means without exception. Moreover there is evidence of a substantial number of luminous X-ray sources hosted by apparently normal galaxies. In this paper the results obtained from multiwavelength observations of hard X-ray selected sources discovered by BeppoSAX and XMM-Newton are presented and briefly discussed.

To understand luminous AGNs in the z < 1 universe, the ASCA AGN samples are the best at present. Combining the identified sample of AGNs from the ASCA Large Sky Survey and Medium Sensitivity Survey, the sample of hard X-ray selected AGNs has been expanded up to 108 AGNs above a flux limit of 10-13 erg s-1 cm-2 in the 2-10 keV hard X-ray band. We discuss the fraction of absorbed AGNs in the hard X-ray selected AGN sample, and the nature of absorbed luminous AGNs.

We present an analysis of X-ray variability in a sample of 156 radio quiet quasars taken from the ROSAT archive, covering a redshift range 0.1 < z < 4.1. Through combining light curves in ensembles we are able to identify trends in variability amplitude with luminosity and with redshift. The decline in variability amplitude with luminosity identified in local AGN (z < 0.1) is confirmed out to z = 2. There is tentative evidence for an increase in QSO X-ray variability amplitude towards high redshifts (z > 2) in the sense that QSOs of the same X-ray luminosity are more variable at z > 2. The simplest explanation for this effect may be that high-redshift QSOs are accreting at a higher efficiency than local AGN.

The REX survey is an ongoing project aimed at the selection of new samples of QSOs and BL Lac objects. Spectroscopic identification of the ~1600 sources in the survey is in progress reaching, so far, about 40% of complete identification level. In this paper, the most recent results derived from the REX survey are briefly summarized.

We have optically identified a complete sub-sample of ROSAT All-Sky Survey (RASS) X-ray sources contained in 6 study areas. Of the original 12° × 12° area near the NEP, only one-quarter was observed until now in order to keep the number of sources to a manageable size. This area is of particular interest because the RASS integration time is about a factor of ten longer than in the other areas and therefore a factor of 3-4 deeper in flux. We have started to observe the RASS sources in the remaining 3/4 of this area. First results are presented.

We report that a volume-limited, X-ray selected AGN sample, including 49 QSO like and starburst galaxies (SBs) at the 0.1-2.4 keV flux level of ≳ 5.3 × 10−14 ergs cm−2 s−1 was formed with photometric redshifts.

Several recent global and Space VLBI surveys of quasars and other types of AGN provide a wealth of material on milli- and sub-milliarcsecond radio structures in hundreds of sources. Results of these projects are presented with an emphasis on the statistics of redshift- and angular-scale-dependent properties of the milli- and sub-milliarcsecond radio structures. These studies make possible disentanglement of intrinsic (possibly, evolutionary) phenomena of parsec-scale radio structures and the imprints of the cosmological model.

We present a short overview of radio surveys for AGN, including the ‘complete’ flux limited surveys and ‘filtered’ surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z = 5.19) and the most luminous z <2 radio galaxy known.

The potential of AGN surveys extends to structure-related objectives: e.g. to study the size and properties of the NLR in AGN. From a complete sample of 1665 radio sources, we selected fifty-five with features on ~0.2-2 kpc scales (core/jet flux ratio <7:1) for further study. Here, we summarize the radio interferometric selection technique used and speculate on the prospects for optical surveys (using a size criterion).

We present new data on Mrk348: 5 GHz data with MERLIN and infrared data with ISO. The radio properties of Mrk 348 are unusual among Seyfert galaxies, and we discuss the orientation of the AGN axis with respect to the line of sight.

A sample of 289 compact radio sources selected from the 7C Catalogue, covering an area of 0.097 steradian, was surveyed at 102 Mhz by the scintillation method. The observations show that the sizes of these sources are less than 0.1” and their flux densities do not exceed 2 Yn. These sources are identified with objects from the FIRST catalogue of radio sources. 99 of these objects have scintillations and have no neighbor in the surrounding 5’. 34 of those 99 are identified with objects on the POSS within 10”×10” areas. 17 of the last 34 are closer to identified POSS objects (within 2”×2” areas). So we suppose that these 17 radio sources are clearly identified with optical sources. Most of them are probably bright quasars. The other 17 will not be discussed here, as we didn’t succeed in their optical identification. There are no POSS objects brighter than 21m in the close surroundings of the remaining 65 radio sources. We have started optical observations of areas close to those 65 objects with the 2.6-m telescope of the Byurakan observatory. Up to now 15 areas were observed. In 5 cases optical objects were found fainter than 22m — 24m within 3” of the compact radio sources (one example is shown in Fig. 1). We are sure that there are no optical objects brihgter than 25m that may be identified with the remaining 10 objects. Those five identifications give us an opportunity to suppose that they are remote quasars. More powerful telescopes than the 2.6-m are needed to perform photometric and spectral observations of similar objects in order to prove our suggestion.

As the first step of the Multiwavelength AGN Survey (MWAS), we have started the FIRST-APM QSO Survey (FAQS). The main goal of FAQS is to compile the most complete sample of bright QSOs, located in the area of the sky covered by the Second Byurakan Survey (SBS). Here we report the current status of an ongoing study based on the cross-identification of the FIRST radio catalog and the APM optical catalog. The overlapping sky area between FIRST and SBS is about 700 deg2. The compiled list of sources for this overlapping region contains ~ 400 quasar candidates brighter than . About 90 objects were already spectroscopically classified. During 1999-2000, we observed spectroscopically more than 150 FAQS objects with the 2.1m telescope of the Guillermo Haro Astropysical Observatory (GHAO). We have found 51 new QSOs (4 BAL QSOs), 13 Seyfert Galaxies (5 NLSyl’s), 23 emission line galaxies, 3 BL Lac objects and 57 stars.

The volumes, equipartition energy density, and radiation losses due to the synchrotron and inverse Compton interactions as a function of redshift and projected linear size of Giant radio galaxies are discussed. The new results are based on data from three samples: 1) Ishwara-Chandra & Saikia (1999), 2) Schoenmakers (Ph.D. Thesis, 1999), and 3) Machalski, Jamrozy & Zola (2001).

Results of monitoring observations at the radio telescope RATAN-600 and a model interpretation of instantaneous 1-22 GHz spectra at six frequencies for 100 selected AGNs are presented. The index of variability at these frequencies is shown for 550 sources monitored in 1997-2001 at 11 epochs. The spectra of the selected sources exhibit flux density variations of about 50% and up. The type of spectral evolution is similar for all the selected objects, favoring the same basic physical model. Model analysis shows that the nature of the radio sources and the observed variability behavior of the spectra can be explained by a model with a relativistic jet of parsec scale in a longitudinal magnetic field.

Measurements of broad-band 6-frequency 1-22 GHz spectra of 660 compact extragalactic radio sources were performed in 1997 (for declinations −30° < δ < + 43°) and 1998 (north of+49°) at RATAN-600. “Average rest-frame” statistical spectral shapes for different subsamples of sources are analyzed. These shapes and each spectrum observed can be represented as the sum of a spectrum of an extended optically thin component (magnetized envelope/lobe), constant or slowly variable and dominating at lower frequencies, and a spectrum of a compact component (relativistic jet), dominating at higher frequencies, with any type of variability. We have revealed specific radio features of the EGRET sub-sample; this favors the models suggesting a relation between the emission mechanisms in radio and gamma-ray ranges. Sources are sampled for which the most compact VLBI structure is expected.

Extragalactic radio sources have been studied for many years, but it is still unclear how they are formed and evolve. The sizes of the most powerful radio emitters in the Universe vary from less than one parsec to more than 1 Mpc. This large range of sizes has been interpreted as evidence for the evolution of the linear sizes of radio structure (e.g., O’Dea and Baum, 1997). A crucial element in the study of their evolution is the identification of the young compact counterparts of “old” FRI/FRII extended objects. Good candidates for young radio sources are those with peaked spectra (Gigahertz Peaked Spectrum - GPS and Compact Steep Spectrum - CSS, e.g., O’Dea 1998). Radio sources are presumably born in the very compact GPS phase, then they expand beyond 1 kpc into the CSS regime and finally, they reach a size of 20 kpc, and afterwards evolve into large-scale radio sources (young scenario, e.g., O’Dea 1998). Alternatively, GPS sources may be compact because a particularly dense environment prevents them from growing larger (old scenario, e.g., O’Dea 1998). In either scenario, the radio source host galaxy determines the time evolution of the radio structure. By studying the optical environments and host galaxies we hope to obtain clues to the evolution of the radio sources. Similarities or differences in host galaxy properties over a range of radio source types and sizes enable us to investigate possible differences or similarities of the radio size class as a whole.

Since 1992 we have been conducting a 5-GHz VLBI imaging survey of southern and equatorial radio sources. So far, we have published the results of two observing sessions with 26 southern radio sources imaged in total (Shen et al. 1997; 1998). In this paper, we present the preliminary results of the third session of observations of 7 equatorial sources in the sample.

Radio sources from the decametric UTR-2 catalog were cross-identified with other radiocatalogs at higher frequencies. We used the CATS database to extract all sources within the UTR beam size (~40’) to find candidate radio identifications. Using the least squares method, we fitted the spectrum of each source with one of a set of curves. We extracted NVSS and FIRST radio images for the radio-identified sources, and looked for a possible relation between size and spectral index.

The steep spectrum of IRAS F02044+0957 was obtained with the RATAN-600 radio telescope at four frequencies. Optical spectroscopy of the system components was carried out with the 2.1m telescope of the Guillermo Haro Observatory. The observational data allow us to conclude that this object is a pair of interacting galaxies, a LINER and an H II galaxy, at z = 0.093.

About 100 steep-spectrum radio sources from the RATAN-600 RC catalog were mapped by the VLA and identified with optical objects down to 24m–25m in the R band using the 6-m telescope. An updated list of calibrators with known redshifts of the same class of RGs was compiled to evaluate the accuracy of photometric redshift estimates. BVRI photometry for 60 RC objects was performed with the 6-m telescope, and by standard model fitting we have estimated color redshifts and ages of the stellar populations of the host gE galaxies. The mean redshift of FR II RGs from the RC list turned out to be ≈1. Several objects were found in which active star formation began in the first billion years after the Big Bang.