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V. I. Zhdanov

Publications and source records attributed to V. I. Zhdanov.

32 records · Page 2Linked to original sources
arXiv2012

Gravitational lens equation. Critical solutions and magnification near folds and cusps

We study approximate solutions of the gravitational lens equation and corresponding lens magnification factor near the critical point. This consideration is based on the Taylor expansion of the lens potential in powers of coordinates and an introduction of a proximity parameter characterising the closeness of a point source to the caustic. Second-order corrections to known approximate solutions and magnification are found in case of a general fold point. The first-order corrections near a general cusp are found as well. Key words: gravitational lensing, methods: analytical

astro-ph.CO↗
arXiv2012

One-dimensional model of cosmological perturbations: direct integration in the Fourier space

We propose a method of calculation of the power spectrum of cosmological perturbations by means of a direct numerical integration of hydrodynamic equations in the Fourier space for a random ensemble of initial conditions with subsequent averaging procedure. This method can be an alternative to the cosmological N-body simulations. We test realizability of this method in case of one-dimensional motion of gravitating matter pressureless shells. In order to test the numerical simulations, we found an analytical solution which describes one-dimensional collapse of plane shells. The results are used to study a nonlinear interaction of different Fourier modes.

astro-ph.CO↗
arXiv2012

Power spectrum of radiation from a Gaussian source microlensed by a point mass: analytic results

Gravitational lensing deals with general-relativistic effects in the propagation of electromagnetic radiation. We consider wavelength-dependent contributions in case of a (micro)lensing of an extended Gaussian source by a point mass under standard assumptions about the incoherent emission of different source elements. Analytical expressions for the power spectrum of a microlensed radiation, which are effective in case of a large source, are obtained. If the source center, the mass, and an observer are on a straight line, the power spectrum is found in a closed form in terms of a hypergeometric function. In the case of general locations of the lens and the source, the result is presented in the form of a series. Approximate analytic expressions for the power spectrum in the case of a large source and high frequencies are obtained.

astro-ph.GA↗
arXiv2011

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 nontrivial corrections we had to go beyond the approximation orders earlier used by Keeton et al. and to take into account the Taylor expansion of the lens equation near 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 a vicinity of the high amplification events (HAEs). We show that the introduction of some "post-linear" corrections reduces chi^2 by 30% 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. Key words: gravitational lensing: micro - quasars: individual (Q2237+0305) - gravitational lensing: strong - methods: analytical

astro-ph.CO↗
arXiv2011

Caustic Crossing Events and Source Models in Gravitational Lens Systems

High amplification events (HAEs) are common phenomena in extragalactic gravitational lens systems (GLSs), where the multiple images of a distant quasar are observed through a foreground galaxy. There is a considerable brightness magnification in one of the quasar images during HAE. Grieger, Kayser, and Refsdal (1988) proposed to use HAEs to study the central regions of quasars in GLSs. In this paper, we consider some problems concerning the identification of different source types on the basis of the HAE observations. We compare the results of light curve simulations to estimate a feasibility to distinguish different source models in GLSs. Analytic approximation methods yielding solutions of the lens equation in a vicinity of fold caustic crossing events are presented. The results are used to obtain amplification factors, which the higher-order corrections for the Gaussian, power-law, and limb-darkening models of a source take into account.

astro-ph.CO↗
arXiv2010

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

We analyze 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 $β=0.63\pm0.10$ with the linear bias $b=1.44\pm0.22$ that marginally (within 2$σ$) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasars velocities (different from the large-scale infall). We note rather slight dependence of quasars velocity dispersion upon the 2pCF parameters in the region $r<2$ Mpc.

astro-ph.CO↗
arXiv2008

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 (power-law kinetic term + power-law potential). 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 $Ω_m$. To remove this degeneracy additional information is needed beyond the data on large-scale geometry.

astro-ph↗
arXiv2008

Q2237+0305 in X-rays: spectra and variability with XMM-Newton

X-ray observations of gravitationally lensed quasars may allow us to probe the inner structure of the central engine of a quasar. Observations of Q2237+0305 (Einstein Cross) in X-rays may be used to constrain the inner structure of the X-ray emitting source. Here we analyze the XMM-Newton observation of the quasar in the gravitational lens system Q2237+0305 taken during 2002. Combined spectra of the four images of the quasar in this system were extracted and modelled with a power-law model. Statistical analysis was used to test the variability of the total flux. The total X-ray flux from all the images of this quadruple gravitational lens system is 6 x 10^{-13} erg/cm2/s in the range 0.2-10 keV, showing no significant X-ray spectral variability during almost 42 ks of the observation time. Fitting of the cleaned source spectrum yields a photon power-law index of Gamma=1.82+0.07/-0.08. The X-ray lightcurves obtained after background subtraction are compatible with the hypothesis of a stationary flux from the source.

astro-ph↗
arXiv2006

Non-metric Generalizations of Relativistic Gravitational Theory and Observational Data Interpretation

We discuss theoretical formalisms concerning with experimental verification of General Relativity (GR). Non-metric generalizations of GR are considered and a system of postulates is formulated for metric-affine and Finsler gravitational theories. We consider local observer reference frames to be a proper tool for comparing predictions of alternative theories with each other and with the observational data. Integral formula for geodesic deviation due to the deformation of connection is obtained. This formula can be applied for calculations of such effects as the bending of light and time-delay in presence of non-metrical effects.

gr-qc↗
arXiv2006

Angular Correlation Function of Quasars from SDSS DR3

We estimate the two-point angular correlation function (CF) of quasars from SDSS DR3 using a special method of comparison random catalog generation. The best-fit value for the CF power-law index is found to be $α=0.78\pm0.18$ on the $2<θ<250$ $arcmin$ interval. This is lower (though in marginal agreement) than earlier result of \markcite{{\it Myers et al.} (2005)} based on SDSS DR1 catalogue of photometrically-classified quasars.

astro-ph↗
arXiv2005

Ultra-Relativistic Expansion of Ideal Fluid with Linear Equation of State

We study solutions of the relativistic hydrodynamical equations, which describe spherical or cylindrical expansion of ideal fluid. We derived approximate solutions involving two arbitrary functions, which describe asymptotic behavior of expanding fireballs in ultra-relativistic limit. In case of a sufficiently stiff linear equation of state the solution may be represented in form of an asymptotic series.

hep-ph↗
arXiv2004

Distant source image motion due to gravitational field of the Galaxy stars

Gravitational field of stars of the Galaxy causes additional motions of images of extragalactic sources. For typical realization of stars this results in a small rotation of extragalactic reference frame in the direction of Galactic rotation. We estimate angular velocity of corresponding image motion and show that it is different in case of discrete and continuous matter distribution in the Galaxy.

astro-ph↗
arXiv2004

Viscous Flows and Conditions for Existence of Shocks in Relativistic Magnetic Hydrodynamics

We present a criterion for a shock wave existence in relativistic magnetic hydrodynamics with an arbitrary (possibly non-convex) equation of state. The criterion has the form of algebraic inequality that involves equation of state of the fluid; it singles out the physical solutions and it can be easily checked for any discontinuity satisfying concervation laws. The method of proof uses introduction of small viscosity into the coupled set of equations of motion of ideal relativistic fluid with infinite conductivity and Maxwell equations.

astro-ph↗