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Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the period 1995–2009. In 1995–2000, the optical brightness of the galactic nucleus changed almost by 1 m in the U band. In 2000–2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a power law SF(τ) ∼ τ b , where τ is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably, their slopes differ markedly: b = 1.34 ± 0.06 and b = 0.25 ± 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6–8 days and on time scales of about 90 days. The observed structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with duration ω as n(ω) ∼ ω α and whose amplitudes depend on duration as A(ω) ∼ ω β. The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3σ confidence level.

Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy 3C 120 over the period 1996–2008. The relative variability amplitude in the U and B bands without any subtraction of the contribution from the underlying galaxy is 23 and 22%, respectively, against 21% in the X-ray band. The autocorrelation function based on the B-band data is considerably wider than that based on the X-ray data. The structure functions on a time scale from 1 to ∼100–300 days in the X-ray and optical spectral ranges have the form of a power law (SF ∼ τb). However, their indices differ significantly: b = 0.42 in the X-ray band and b = 1.36 in the B band. Considering the X-ray and optical variabilities as a superposition of independent flares in a wide range of durations, we may conclude that the amplitudes of short flares in the X-ray band are higher than those in the optical one and, conversely, the relative amplitudes of long flares in the X-ray band are slightly lower than those in the optical one, i.e., short events dominate in the X-ray band. The optical flux variations in the Rc and Ic bands lag significantly behind those in the B band, by 3.9−0.7+1.0 and 6.2−0.6+1.1 days, respectively, if the lag is estimated from the centroid of the cross-correlation function. The X-ray variability on a time scale of about 1800 days (∼5 yr) lags behind the B-band variations by 5.3−3.3+2.7 days, but the confidence level of this estimate is only 87%. A more detailed analysis of the correlation between the X-ray and optical emissions has revealed a fairly complex picture: different degrees of correlation between the optical and X-ray fluxes are observed at different times.

We analyze the spectroscopic and photometric observations of the active galactic nucleus (AGN) 1E 0754.6+3928 performed at Crimean Astrophysical Observatory in 1998–2004. Based on formal spectroscopic criteria for the optical wavelength range, we can classify this object as a narrow-line Seyfert 1 (NLS1) galaxy. Over the period of its observations, the AGN 1E 0754.6+3928 showed a very low rms flux variability amplitude in both continuum and Hβ (∼3%). The Hβ time lag relative to the continuum has been found from the cross-correlation function centroid to be τ cent = 112 −67 +215 days. This result and the Hβ line dispersion estimate have allowed us to determine the central black hole mass by the reverberation method: 1.05 × 108 M ⊙. The position of 1E 0754.6+3928 in the black hole mass-luminosity diagram agrees with the positions of other NLS1 galaxies and can be explained by an enhanced mass accretion rate in the central source.

We discuss the integrated kinematic parameters of 20 M51-type binary galaxies. A comparison of the orbital masses of the galaxies with the sum of the individual masses suggests that moderately massive dark halos surround bright spiral galaxies. The relative velocities of the galaxies in binary systems were found to decrease with increasing relative luminosity of the satellite. We obtained evidence that the Tully-Fisher relation for binary members could be flatter than that for local field galaxies. An enhanced star formation rate in the binary members may be responsible for this effect. In most binary systems, the direction of orbital motion of the satellite coincides with the direction of rotation of the main galaxy. Seven candidates for distant M51-type objects were found in the Northern and Southern Hubble Deep Fields. A comparison of this number with the statistics of nearby galaxies provides evidence for the rapid evolution of the space density of M51-type galaxies with redshift Z. We assume that M51-type binary systems could be formed through the capture of a satellite by a massive spiral galaxy. It is also possible that the main galaxy and its satellite in some of the systems have a common cosmological origin., Comment: 8 pages, 4 figures, to be published in Astronomy Letters

Spectroscopic observations of twelve M51-type binary galaxies with the 6-m Special Astrophysical Observatory telescope are presented. We constructed the rotation curves for the primary galaxies of each binary system and determined the line-of-sight velocities of their companions from the Hα and [N II] 6583 A emission lines.