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The Russian Academy of Sciences and Federal Space Agency, together with the participation of many international organizations, worked toward the launch of the RadioAstron orbiting space observatory with its onboard 10-m reflector radio telescope from the Baikonur cosmodrome on July 18, 2011. Together with some of the largest ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna ground-space radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes, accretion disks, and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The results of ground-based and inflight tests of the space radio telescope carried out in both autonomous and ground-space interferometric regimes are reported. The derived characteristics are in agreement with the main requirements of the project. The astrophysical science program has begun., 54 pages, 11 figures; published by Astronomicheskij Zhurnal (in Russian) and Astronomy Reports (in English)

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).

Radio data from four extragalactic sources, three quasars and one galaxy, show evidence for an apparent expansion faster than the speed of light. The data on these ‘superluminal’ sources are reviewed, and their implications briefly discussed.

Il semble que les changements de la densite de flux soient provoques par une combinaison d'une polarisation rectiligne exceptionnellement elevee et d'une rotation Faraday ionospherique variable

The bright radio nucleus 3C84 of the peculiar galaxy NGC1275 was among the first sources studied by VLBI techniques sixteen years ago (Clark et al., 1968). Early observations at short centimeter wavelengths using arrays of up to four telescopes (Schilizzi et al., 1975, and references therein) demonstrated the presence of structure significantly more complex than that seen in other strong compact objects, but were insufficient to determine the brightness distribution with the relatively primitive methods then in use. By the time of the most recent international VLBI symposium (Aug. 1978, in Heidelberg, FRG), Pauliny-Toth et al. (1976) had succeeded in modelling the structure seen by a 4-station transatlantic array, revealing three distinct bright emission regions aligned in position angle −9°, and connected by non-colinear, more diffuse features. Further observations and a reanalysis of earlier data by Preuss et al. (1979) confirmed previous inferences that the three major condensations remained stationary but varied in brightness.

The radio nucleus of NGC1275 (3C84) is found to consist of three apparently stationary centres of emission extending over 0.006″ (3pc) along position angle −9°. One or more of these centres have changed their intensity or size in the last 3 yr. A preferential direction of alignment of both the small scale and large scale radio features as well as the optical features suggests a common cause of alignment operating over linear distances from a few pc to > 100 kpc.

The discovery1 of radio structure on a scale of 10–50 m arc s in SS433 has prompted us to monitor the object with the European VLBI network. The first observations in this programme were made for periods of 9 and 10 h at a wavelength of 6 cm on 9 January (JD2444248) and 1–2 June (JD2444392.5) 1980. Our results, together with the observations of Walker et al.2 at an earlier epoch, show that the compact radio structure of SS433 changes orientation in a manner consistent with the 164-day precession period inferred from the optical emission lines, but with a phase delay of 5 ± 4 days. The shape of the radio structure is elongated, non-linear and changes from one observing epoch to the other.

A campaign of VLBI observations of SS433 using the European network vas begun in January 1980 and since October 1980 has continued at intervals of about two months except for the last two observations which were 6 days apart, see Table 1. The results of the first two epochs have been published in Nature (ref. 1), and those of the following six epochs are being prepared for publication.

The normal spiral galaxy M81, which has some characteristics of a Seyfert (Peimbert, Torres-Peimbert, 1981) has a flat spectrum in the radio range (de Bruyn et al., 1976), variable on the time scale of days (Crane et al., 1976), and detectable radiation at infrared (Rieke, Lebofsky, 1978) and X-ray wavelengths (Elvis, van Speybroeck, 1981). At a distance of ∿3.3 Mpc, M81 is the nearest extragalactic object with a nucleus detectable with VLBI (Kellermann et al., 1976). We report here on simultaneous VLBI observations made with the Mark III system at 2.3 and 8.3 GHz. Observations on 14 and 16 March 1981 utilized the 100 m diameter telescope in Effelsberg, W. Germany (MPIR); the 43 m telescope at Green Bank, WV (NRAO); and the 40 m telescope near Big Pine, CA (OVRO).

The Bologna group has been carrying on a monitoring program at 408 MHz of more than a hundred sources since 1975. Among sources found to be variable or possibly variable (Fanti et al., 1983) a small sample (10) has steep spectrum (α∿ 0.6, S ∝ν-α) in the frequency range 0.4–15 GHz.

The flux variability of extragalactic radio sources at decimetric wavelengths (Low Frenquency Variability — LFV) is mostly associated with the cores of compact radio sources.

We present 18 cm VLBI observations of a sample of compact radio sources, selected on the basis of low frequency variability.

SS433 has been observed extensively in virtually all wavelength regimes. In the X-ray (Seward et al. 1979) and the radio (Hjellming and Johnston, 1981a, b, 1982; Spencer 1979, Schilizzi et al. 1981, 1982; Niell et al. 1981, 1982) there is clear evidence of jets emanating from the central star system in the direction of the well-known extensions in the surrounding shell of emission, W50. Our VLBI observations of SS433 in 1980 and 1981 were made at wavelengths ranging from 6 to 21 cm (beamsizes of 10 to 100 milli-arcsec or ∿ 1015 to 1016 cm at the distance of W50) and had sufficient resolution to distinguish individual blobs of emission in the jets. An example is shown in Fig. 1

The extremely powerful compact radio nucleus of NGC1275 is perhaps the most complex structure seen at milliarcsecond scales. Early attempts to determine its structure (Schilizzi et al. 1975) were unsuccessful, although it was evident that the structure consisted of several bright regions whose relative positions remained fixed while their intensities varied. Later observations and analysis (Pauliny-Toth et al. 1976; Preuss et al. 1979) confirmed this inference and revealed a slow expansion in a direction transverse to the primary axis of alignment.

The extremely powerful compact radio nucleus of NGC1275 is perhaps the most complex structure seen at milliarcsecond scales. Early attempts to determine its structure (Schilizzi et al. 1975) were unsuccessful, although it was evident that the structure consisted of several bright regions whose relative positions remained fixed while their intensities varied. Later observations and analysis (Pauliny-Toth et al. 1976; Preuss et al. 1979) confirmed this inference and revealed a slow expansion in a direction transverse to the primary axis of alignment.

Mark III very long baseline interferometry (VLBI) observations have been made of the nucleus in the normal galaxy M81 (NGC 3031) simultaneously at 2.3 and 8.3 GHz, and it was found that nearly 100% of the flux density of the nuclear region originates in an elongated radio core with linear dimensions 1000-4000 AU, dependent on frequency. This galactic nucleus is the most compact observed in any extragalactic source. The position coincides with that of the nucleus at optical and X-ray wavelengths within the larger uncertainties of the latter two. The position angle of the major axis of the M81 nucleus is within 3 deg of 75 deg at 2.3 GHz and within 6 deg of 50 deg at 8.3 GHz and is frequency dependent at the 4 sigma level. These values straddle the 62 deg position angle of the projection on the sky of the rotation axis of the galaxy. The spectrum of the core is slightly inverted, and the length of its major axis decreases with frequency. These results are consistent with the emission's being incoherent electron synchrotron radiation from an inhomogeneous region with an optical depth varying along the rotation axis of the galaxy.

A three-station VLBI Galactic H I absorption experiment has been carried out with baselines up to 600 km. The large collecting area of the European VLBI Network consisting of the Lovell Telescope (Mark Ia), the 100 m telescope at Effelsberg, and the Westerbork Synthesis Radio Telescope was necessary to achieve adequate sensitivity for these high angular resolution (0.05 arcsec) and high-velocity resolution (0.5 km/s) observations. The extragalactic sources 3C 138, 3C 147, and 3C 380 were observed. Changes in the local H I apparent absorption were observed in all three sources as a function of resolution. The changes are most striking in the direction of 3C 138. The implied linear diameters are in the range 25 AU with typical H I densities of 10,000-100,000/cu cm. 19 refs.