A. E. Vol’vach

Correlations between the development of a flare in the Blazar 3C 454.3 in the radio and optical

Radio and optical data are used to analyze the development of the flare in the blazar 3C 454.3 observed in 2004–2007. A detailed correspondance between the optical and radio flares is established, with a time delay that depends on the observing frequency. The variation of the delay of the radio flare relative to the optical flare is opposite to the dispersion delay expected for the propagation of radiation in the interstellar medium, testifying to an intrinsic origin for the observed outburst. Small-scale flux variations on time intervals of 5–10 days in the millimeter and optical are also correlated, with a time delay of about ten months. This may provide evidence for a single source generating the radiation at all wavelengths. Rapid flux fluctuations in the radio and optical that are correlated with the indicated time delays could be associated with inhomogeneities in the accretion disk. Detailed studies of the flux variations of Active Galactic Nuclei (AGN) can be used to analyze the structure of the accretion disk. A model for the energy release in AGN that is not associated purely with accretion onto supermassive black holes is proposed. As is the case for other active members of the AGN family, estimates of the lifetime of the binary black-hole system in 3C 454.3 suggest that this object is in a stage of its evolution that is fairly close to the coalescence of its black holes. The energy that is released as the companion of the central black hole loses orbital angular momentum is sufficient to explain the observed AGN phenomena. The source of primary energy release could be heating of the gas behind shock fronts that arise due to the friction between the companion black hole and the ambient gaseous medium. The orbit of the companion could be located at the periphery of the accretion disk of the central body at its apocenter and plunge more deeply into the accretion disk at its pericenter, inducing flares at all wavelengths. Energy-release parameters such as the temperature and density of the heated gas are estimated for 3C 454.3. The model considered assumes omnidirectional radiation of the medium in the presence of a magnetic field. The radiation corresponding to the minimum flux level (base level) could represent omnidirectional radiation due to the orbit of the moving companion. The fraction of the energy that is transferred to directed jets is small, comprising 1–2% of the total energy released due to the loss of orbital angular momentum by the companion.

Sub-parsec structure of binary supermassive black holes in active galactic nuclei

Long-term, multi-frequency monitoring of the radio fluxes of the four BL Lac objects 3C 120, OJ 287, 1308+326, and BL Lac is considered. Harmonic components of the flux variability on scales from one year to decades are determined. The observational data used were obtained at the Radio Astronomy Laboratory of the Crimean Astrophysical Observatory (Ukraine) and the University of Michigan Radio Astronomy Observatory (USA). These data are used to construct kinematic models for active galactic nuclei using values for the orbital and precessional periods of binary systems consisting of supermassive black holes. The derived speeds of the companions in their orbits lie in the narrow range 3000–4000 km/s. The orbital radii for the binary supermassive black holes also lie in a narrow range, 1017–1018 cm, providing evidence that observed prominent examples of active galactic nuclei are fairly close binary systems. The parameters of the mediumin which the components of the binary systems are moving are estimated, as well as the rates at which the systems are losing orbital angular momentum and their lifetimes to coalescence.

Multi-frequency studies of the non-stationary radiation of the blazar 3C 454.3

Long-term monitoring data at five radio frequencies from 4.8 to 37 GHz obtained at the Crimean Astrophysical Observatory, Metsahovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory are used to analyze variations of the flux of the Active Galactic Nucleus (AGN) 3C 454.3. The dynamical characteristics of the three latest powerful flares from 2004 to 2010 are analyzed in detail. Observations in the gamma-ray (0.1–300 GeV), X-ray (2–10 kev, 15–50 keV), and optical are also used. Delays in the development of flares at different frequencies are derived. An empirical frequency dependence for the delays of flares from the gamma-ray to the radio is determined, which can be fit using a logarithmic low and remains the same from flare to flare. The physical characteristics of the central region of the AGN 3C 454.3 are used to estimate the size of its Strömgren sphere, taking into account the relevant mechanisms for heating and cooling the medium, as well as the adopted laws for the variation of the density and temperature with distance from the source of ionization. A model for the location of the radiation regions in the jet at various frequency ranges during the development of flares is proposed.

A multi-frequency study of brightness variations of the blazar 0716+714

Based on long-term monitoring at five radio frequencies between 4.8 and 37 GHz performed at the Radio Astronomy Laboratory of the Crimean Astrophysical Observatory, the University of Michigan Radio Astronomy Observatory, and the Metsähovi Radio Observatory, we have analyzed two flare events in the blazar S5 0716+714 during the last five years. The time separation between the flares is in agreement with data derived earlier from a spectral analysis of flux variations at the above frequencies, which revealed a periodic component with a period of about four years in the variations. We consider the dynamics of strong flares in 2003 and 2007 and determine the delays between the development of the event at various radio frequencies. Our data can be used to draw conclusions about the kinematic and dynamical properties of the source.

Studies of sources from the WMAP catalog

Observations of a complete sample of sources from the WMAP catalog were obtained at 22.2 and 36.8 GHz on the RT-22 radio telescope of the Crimean Astrophysical Observatory. We have determined the distribution of the source spectral indices between these frequencies. The distributions of the spectral indices of the WMAP catalog (between 23 and 33 GHz) and in the RT-22 sample have the same shape and half-width, suggesting that the mean source parameters are constant in time. We have plotted the log N — log S dependence down to the flux levels of about 0.1 Jy using pilot data from the AT20 survey, where a cosmological “cutoff” in the source counts is already observed. The variability of individual sources in connection with flare activity is considered. The optical characteristics of the complete sample of WMAP sources are compared to those of identified AT20 survey sources.

Long-term, multi-frequency monitoring of the blazar S0528+134 (Nimfa)

Flux-density variations of the quasar S0528+134 (Nimfa) are analyzed based on long-term monitoring at five radio frequencies between 4.8 and 37 GHz, performed at the Crimean Astrophysical Observatory, the Metsähovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory. The dynamics of a powerful flare in 1996 are analyzed using gamma-ray (0.1–300 GeV), X-ray (2–10 keV, 15–50 keV), and radio observations. The delays of the flare between different spectral ranges and between different radio wavelengths have been measured. The dependence for the delays at different radio wavelengths relative to the X-ray and optical flares is established based on long-term observations in the X-ray, optical, and radio obtained from 2004 to 2013. Multi-frequency monitoring in the radio is used to estimate the orbital and precession periods in the binary supermassive black hole system S0528+134 and the physical characteristics of this system.

A prolonged flare in the blazar 3C 454.3

We present an analysis of data from multi-frequency monitoring of the blazar 3C 454.3 in 2010–2012, when the source experienced an unusually prolonged flare with a duration of about two years. This corresponds to the orbital period of the companion in a scenario in which two supermassive black holes are present in the nucleus of 3C 454.3. The flare’s shape, duration, and amplitude can be explained as a result of precession, if the plane of the accretion disk and the orbital plane of the binary are coincident. We detected small-scale structure of the flare, on time scales of no more than a month. These features probably correspond to inhomogeneities in the accretion disk and surrounding regions, with sizes of the order of 1015 cm. We estimated the size of the accretion disk based on the dynamical and geometrical parameters of this binary system: its diameter is comparable to the size of the orbit of the supermassive binary black hole, and its thickness does not exceed the gravitational radius of the central black hole. The presence of characteristic small-scale features during the flare makes it possible to estimate the relative time delays of variations in different spectral ranges: from gamma-ray to millimeter wavelengths.

Long-term monitoring of the blazars AO 0235+164 and S5 0716+714 in the optical and radio ranges

Long-term, multi-frequency optical and radio monitoring data for the Active Galactic Nuclei (AGNs) AO 0235+164 and S5 0716+714 are used to derive the characteristics of their radiation on time scales from hours to decades. Structure-function and harmonic analyses are carried out to determine the parameters of the radiation of these AGNs and explain their physical characteristics. Periodic components that could be associated with the motion of companions along an orbit in a close binary system of two supermassive black holes are identified. Both of the analysis methods used yield consistent results for the harmonic components. The results obtained are consistent with the idea that we are viewing systems of two supermassive black holes in a stage of their evolution that is close to coalescence. The substantial energy release of these AGNs can be interpreted as dynamical losses arising during the motion of the companion about the common center of gravity in a dense accreting medium, sometimes crossing through the accretion disk.

Physical characteristics of the Blazar AO 0235+164

Long series of multi-frequency monitoring data of the active galactic nucleus (AGN) AO 0235+164 from the radio to the gamma-ray are analyzed. AO 0235+164 may be a close binary system comprised of two supermassive black holes (SMBHs). A harmonic analysis has established the presence of orbital and precessional periods of two and eight years, respectively. These values are close to the analogous periods found in other AGNs that have been proposed to be close SMBH binary systems in a stage of their evolution close to coalescence. A cross-correlation analysis is used to find the time delay between corresponding flares occurring in different wavebands. The empirical dependence found earlier for a number of other AGNS relating the delay in the flux variations with the frequency is observed for this object, and has the form of an inverse logarithmic dependence, providing evidence that the flux variability of AGNs at centimeter and shorter wavelengths is intrinsic. The standard picture of jet activity of AGNs supposes plasma formations that move from the central regions along outflows, becoming optically thin at longer and longer wavelengths as they do so. The physical and dynamical characteristics of AO 0235+164 suggest it is a close binary with SMBHs with similar masses of the order of 1010M⊙. This is one of the most massive systems of two SMBHs. The velocities of the companion and central black hole about their common center of mass are estimated to be 104 and 5×103 km/s. The results obtained suggest that observed bright AGNs form a relatiavely rare population among massive elliptical galaxies, due to their narrowly directed emission and their short lifetimes.

Investigating statistical and spectral characteristics of the radio sources from the RadioAstron catalog at millimetric wavelengths

We consider some statistical characteristics of radio sources at 22 GHz in the framework of the preparatory works on the RadioAstron space mission. The expected density of radio sources with inverted spectra is estimated. Based on the observations of the radio sources from the preliminary RadioAstron sample, we compare the expected and measured angular densities of the radio sources with inverted spectra. The optical characteristics of the objects with inverted spectra and of the sources from the complete sample are compared as well. We present some spectral parameters of the radio sources observed at two different frequencies. Some conclusions about the completeness and reliability of the preliminary RadioAstron catalog are made.