On a multi-resonant origin of high frequency quasiperiodic oscillations in the neutron-star X-ray binary 4U 1636-53

    by Zdeněk Stuchlík· 01 dubna, 2007· in Fyzika· 0 comments
    The results we presented were biased because of the typing error in the code transcription of the equation (A.12). We will replace by the corrected version soon. The brief of the corrected results can be found at http://www.physics.cz/research/doc/posters/1181038112_0.pdf
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    Humpy LNRF-velocity profiles in accretion discs orbiting rapidly rotating Kerr black holes: a possible relation to epicyclic oscillations

    by Zdeněk Stuchlík· 01 dubna, 2007· in Fyzika· 0 comments
    Coordinate-independent definition of the characteristic, so-called "humpy" frequency related to the positive gradient of the orbital velocity in locally non-rotating frames around nearly extreme Kerr black holes is given and compared with the epicyclic and orbital frequencies for both Keplerian thin discs and limiting marginally stable thick discs.
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    Marginally stable thick discs orbiting the Kerr-de Sitter black holes: the mass estimates

    by Zdeněk Stuchlík· 01 dubna, 2007· in Fyzika· 0 comments
    Basic properties of equipotential surfaces in test perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes are summarized. The central mass-densities of adiabatic non-relativistic tori, for which the approximation of test fluid is adequate, are given and compared with the typical densities of Giant Molecular Clouds.
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    On a multi-resonant origin of high frequency quasiperiodic oscillations in the neutron-star X-ray binary 4U 1636-53

    by Zdeněk Stuchlík· 01 dubna, 2007· in Fyzika· 0 comments
    The results we presented were biased because of the typing error in the code transcription of the equation (A.12). We will replace by the corrected version soon. The brief of the corrected results can be found at http://www.physics.cz/research/doc/posters/1181038112_0.pdf
    Read More

    Humpy LNRF-velocity profiles in accretion discs orbiting almost extreme Kerr black holes. A possible relation to quasi-periodic oscillations

    by Zdeněk Stuchlík· 01 března, 2007· in Fyzika· 0 comments
    Context: Change of sign of the LNRF-velocity gradient has been found for accretion discs orbiting rapidly rotating Kerr black holes with spin a>0.9953 for Keplerian discs and a>0.99979 for marginally stable thick discs. Such a "humpy" LNRF-velocity profiles occur just above the marginally stable circular geodesic of the black hole spacetimes. Aims: Aschenbach (2004) has identified the maximal rate of change of the orbital velocity within the "humpy" profile with a locally defined critical frequency of disc oscillations, but it has been done in a coordinate-dependent form that should be corrected. Methods: We define the critical "humpy" frequency νh in general relativistic, coordinate independent form, and relate the frequency defined in the LNRF to the distant observers. At radius of its definition, the resulting "humpy" frequency νh is compared to the radial νr and vertical νv epicyclic frequencies and the orbital frequency of the discs. We focus our attention to Keplerian thin discs and perfect-fluid slender tori where the approximation of oscillations with epicyclic frequencies is acceptable. Results: In the case of Keplerian discs, we show that the epicyclic resonance radii r3{:1} and r4{:1} (with ν_v{:}ν_r=3{:}1, 4{:}1) are located in vicinity of the "humpy" radius rh where efficient triggering of oscillations with frequencies νh could be expected. Asymptotically (for 1-a<10-4) the ratio of the epicyclic and Keplerian frequencies and the humpy frequency is nearly constant, i.e., almost independent of a, being for the radial epicyclic frequency ν_r{:}νh ˜ 3{:}2. In the case of thick discs, the situation is more complex due to dependence on distribution of the specific angular momentum ℓ determining the disc properties. For ℓ=const. tori and 1-a<10-6 the frequency ratios of the humpy frequency and the orbital and epicyclic frequencies are again nearly constant and independent of both a and ℓ being for the radial epicyclic frequency ν_r{:}νh close to 4. In the limiting case of very slender tori (ℓ˜ℓms) the epicyclic resonance radius r4{:1}˜ rh for all the relevant interval of 1-a<2× 10-4. Conclusions: .The hypothetical "humpy" oscillations could be related to the QPO resonant phenomena between the epicyclic oscillations in both the thin discs and marginally stable tori giving interesting predictions that have to be compared with QPO observations in nearly extreme Kerr black hole candidate systems. Generally, more than two observable oscillations are predicted.
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    Humpy LNRF-velocity profiles in accretion discs orbiting almost extreme Kerr black holes. A possible relation to quasi-periodic oscillations

    by Zdeněk Stuchlík· 01 března, 2007· in Fyzika· 0 comments
    Context: Change of sign of the LNRF-velocity gradient has been found for accretion discs orbiting rapidly rotating Kerr black holes with spin a>0.9953 for Keplerian discs and a>0.99979 for marginally stable thick discs. Such a "humpy" LNRF-velocity profiles occur just above the marginally stable circular geodesic of the black hole spacetimes.
    Aims: Aschenbach (2004) has identified the maximal rate of change of the orbital velocity within the "humpy" profile with a locally defined critical frequency of disc oscillations, but it has been done in a coordinate-dependent form that should be corrected.
    Methods: We define the critical "humpy" frequency νh in general relativistic, coordinate independent form, and relate the frequency defined in the LNRF to the distant observers. At radius of its definition, the resulting "humpy" frequency νh is compared to the radial νr and vertical νv epicyclic frequencies and the orbital frequency of the discs. We focus our attention to Keplerian thin discs and perfect-fluid slender tori where the approximation of oscillations with epicyclic frequencies is acceptable.
    Results: In the case of Keplerian discs, we show that the epicyclic resonance radii r3{:1} and r4{:1} (with ν_v{:}ν_r=3{:}1, 4{:}1) are located in vicinity of the "humpy" radius rh where efficient triggering of oscillations with frequencies νh could be expected. Asymptotically (for 1-a<10-4) the ratio of the epicyclic and Keplerian frequencies and the humpy frequency is nearly constant, i.e., almost independent of a, being for the radial epicyclic frequency ν_r{:}νh ∼ 3{:}2. In the case of thick discs, the situation is more complex due to dependence on distribution of the specific angular momentum ℓ determining the disc properties. For ℓ=const. tori and 1-a<10-6 the frequency ratios of the humpy frequency and the orbital and epicyclic frequencies are again nearly constant and independent of both a and ℓ being for the radial epicyclic frequency ν_r{:}νh close to 4. In the limiting case of very slender tori (ℓ∼ℓms) the epicyclic resonance radius r4{:1}∼ rh for all the relevant interval of 1-a<2× 10-4.
    Conclusions: .The hypothetical "humpy" oscillations could be related to the QPO resonant phenomena between the epicyclic oscillations in both the thin discs and marginally stable tori giving interesting predictions that have to be compared with QPO observations in nearly extreme Kerr black hole candidate systems. Generally, more than two observable oscillations are predicted.
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    Optical reference geometry and inertial forces in Kerr de Sitter spacetimes

    by Zdeněk Stuchlík· 01 února, 2007· in Fyzika· 0 comments
    Optical reference geometry and the related concept of inertial forces are investigated in Kerr de Sitter spacetimes. Properties of the inertial forces are summarized and their typical behaviour is illustrated. The intuitive 'Newtonian' application of the forces in the relativistic dynamics is demonstrated in the case of the test particle circular motion, static equilibrium positions and perfect fluid toroidal configurations. Features of the optical geometry are illustrated by the embedding diagrams of its equatorial plane. The embedding diagrams do not wholly cover the stationary regions of the spacetimes, therefore the limits of embeddability are established. The shape of the embedding diagrams is related to the behaviour of the centrifugal force and it is characterized by the number of turning points of the diagrams. Discussion of the number of embeddable photon circular orbits is also included and the typical embedding diagrams are constructed. The Kerr de Sitter spacetimes are classified according to the properties of the inertial forces and embedding diagrams.
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    Optical reference geometry and inertial forces in Kerr de Sitter spacetimes

    by Zdeněk Stuchlík· 01 února, 2007· in Fyzika· 0 comments
    Optical reference geometry and the related concept of inertial forces are investigated in Kerr de Sitter spacetimes. Properties of the inertial forces are summarized and their typical behaviour is illustrated. The intuitive 'Newtonian' application of the forces in the relativistic dynamics is demonstrated in the case of the test particle circular motion, static equilibrium positions and perfect fluid toroidal configurations. Features of the optical geometry are illustrated by the embedding diagrams of its equatorial plane. The embedding diagrams do not wholly cover the stationary regions of the spacetimes, therefore the limits of embeddability are established. The shape of the embedding diagrams is related to the behaviour of the centrifugal force and it is characterized by the number of turning points of the diagrams. Discussion of the number of embeddable photon circular orbits is also included and the typical embedding diagrams are constructed. The Kerr de Sitter spacetimes are classified according to the properties of the inertial forces and embedding diagrams.
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    A virtual trip to the Schwarzschild-de Sitter black hole

    by Zdeněk Stuchlík· 01 prosince, 2006· in Fyzika· 0 comments
    We developed realistic fully general relativistic computer code for simulation of optical projection in a strong, spherically symmetric gravitational field. Standard theoretical analysis of optical projection for an observer in the vicinity of a Schwarzschild black hole is extended to black hole spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitter spacetimes. Influence of the cosmological constant is investigated for static observers and observers radially free-falling from static radius. Simulation includes effects of gravitational lensing, multiple images, Doppler and gravitational frequency shift, as well as the amplification of intensity. The code generates images of static observers sky and a movie simulations for radially free-falling observers. Techniques of parallel programming are applied to get high performance and fast run of the simulation code.
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    A virtual trip to the Schwarzschild-de Sitter black hole

    by Zdeněk Stuchlík· 01 prosince, 2006· in Fyzika· 0 comments
    We developed realistic fully general relativistic computer code for simulation of optical projection in a strong, spherically symmetric gravitational field. Standard theoretical analysis of optical projection for an observer in the vicinity of a Schwarzschild black hole is extended to black hole spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitter spacetimes. Influence of the cosmological constant is investigated for static observers and observers radially free-falling from static radius. Simulation includes effects of gravitational lensing, multiple images, Doppler and gravitational frequency shift, as well as the amplification of intensity. The code generates images of static observers sky and a movie simulations for radially free-falling observers. Techniques of parallel programming are applied to get high performance and fast run of the simulation code.
    Read More
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