V. I. Zhdanov

Correlation function of quasars in real and redshift space from the Sloan Digital Sky Survey Data Release 7

We analyse the quasar two-point correlation function (2pCF) within the redshift interval 0.8 10 h -1 Mpc, the parameter describing the large-scale infall to density inhomogeneities is β = 0.63 ± 0.10 with the linear bias b = 1.44 ± 0.22, which marginally (within 2σ) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasar velocities (different from the large-scale infall). We note a slight dependence of the quasar velocity dispersion upon the 2pCF parameters in the region r < 2 Mpc.

Asymptotic expansions and amplification of a gravitational lens near a fold caustic

We propose two methods that enable us to obtain approximate solutions of the lens equation near a fold caustic with an arbitrary degree of accuracy. We obtain ‘post-linear’ corrections to the well-known formula in the linear caustic approximation for the total amplification of two critical images of a point source. In this case, in order to obtain the non-trivial corrections we have to go beyond the approximation orders earlier used by Keeton et al. and to perform the Taylor expansion of the lens equation near the caustic up to the fourth order. Corresponding analytical expressions are derived for the amplification in cases of the Gaussian and power-law extended source models; the amplifications depend on three additional fitting parameters. Conditions of neglecting the correction terms are analysed. The modified formula for the amplification is applied to the fitting of light curves of the Q2237+0305 gravitational lens system in the vicinity of the high amplification events (HAEs). We show that the introduction of some ‘post-linear’ corrections reduces χ2 by 30 per cent in the case of known HAE on the light curve of image C (1999). These corrections can be important for a precise comparison of different source models with regard for observational data.

Gravitational microlensing as a probe for dark matter clumps

Extended dark matter (DM) substructures may play the role of microlenses in the Milky Way and in extragalactic gravitational lens systems (GLSs). We compare microlensing effects caused by point masses (Schwarzschild lenses) and extended clumps of matter using a simple model for the lens mapping. A superposition of the point mass and the extended clump is also considered. For special choices of the parameters, this model may represent a cusped clump of cold DM, a cored clump of self-interacting dark matter (SIDM) or an ultra compact minihalo of DM surrounding a massive point-like object. We built the resulting micro-amplification curves for various parameters of one clump moving with respect to the source in order to estimate differences between the light curves caused by clumps and by point lenses. The results show that it may be difficult to distinguish between these models. However, some region of the clump parameters can be restricted by considering the high amplification events at the present level of photometric accuracy. Then we estimate the statistical properties of the amplification curves in extragalactic GLSs. For this purpose, an ensemble of amplification curves is generated yielding the autocorrelation functions (ACFs) of the curves for different choices of the system parameters. We find that there can be a significant difference between these ACFs if the clump size is comparable with typical Einstein radii; as a rule, the contribution of clumps makes the ACFs less steep.

Evidence for a binary black hole in active nucleus of NGC 1194 galaxy

Based on the data obtained with the XMM-Newton and INTEGRAL space telescopes, some properties of the X-ray emission from active nucleus of NGC 1194 galaxy are analyzed. Particular attention is paid to the X-ray energy spectrum from 6 to 7.5 keV. In this case, besides FeKα (6.38 keV) and FeKβ (7.01 keV) fluorescent lines, an additional line with an energy of 6.51 keV was found with a rather broad profile generated in an inclined accretion disk, which is characteristic for the FeKα relativistic line. Such a line configuration can be explained within the model of binary black hole system in the nucleus of NGC 1194 with orbital period of the order of 6 years. The energies and profiles of the iron FeKα spectral lines correspond to the radiation of accretion disks around the Schwazschild black holes with inclination angles of 6–20 degrees between the line of sight and the normal to the disk. To make final conclusions about the line structure and the presence or absence of a binary black hole in the nucleus of NGC 1194, it is necessary to perform additional observations.

Statistics of light curves of a distant source microlensed by a system of point and extended masses

Gravitational microlensing of a distant source by a stochastic system of point masses (stars) and extended masses that model dark-matter clumps is analyzed. The size of each clump is set to be equal to 5 or 10 Einstein radii. A total of 100 realizations of the magnification map are generated under the assumption of a spatially homogeneous distribution of lenses with the Salpeter mass function for each set of parameters (optical microlensing depth and the clump size). Autocorrelation functions of light curves for different relative contributions of clumps to the total microlensing optical depth σtot = 0.3 are calculated on this basis. It is demonstrated that the dependence of autocorrelation functions on the optical depth of clumps is nonmonotonous.

Cosmological scalar fields that mimic the ΛCDM cosmological model

We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard ΛCDM cosmological model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric distance and angular diameter distance as functions on z). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and separable scalar field Lagrangians; the cases of power-law kinetic term and power-law potential are considered. Exact analytic solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some degeneracy leading to lower precision in determination of Ωm. To remove this degeneracy additional information is needed besides the data on large-scale geometry.

Ballistic and diffusive components in the dynamic spectra of ultrahigh energy cosmic rays from nearby transient sources

Ultrahigh energy cosmic rays (UHECRs, E > 1018 eV) from extragalactic sources deviate in the galactic and intergalactic magnetic fields, which explains the diffusive character of their propagation, the isotropization of their total flux, and the absence of UHECR clusters associated with individual sources. Extremely high energy cosmic rays (E > 1019.7 eV) are scattered mainly in localized magnetized structures, such as galaxy clusters, filaments, etc., with a mean free path of tens of megaparsecs; therefore, in the case of nearby transient sources, a substantial contribution to the observed flux is expected from unscattered and weakly scattered particles, which may be a decisive factor in the identification of these sources. We propose a method for calculating the time evolution of the UHECR energy spectra based on analytical solutions of the transport equation with the explicit determination of the contributions from scattered and unscattered particles. As examples, we consider the cases of transient activity of the nearest active galactic nucleus, Centaurus A, and the acceleration of UHECRs by a young millisecond pulsar.