QPOs in Microquasars: the Spin Problem

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    In Galactic microquasars with double-peak kHz quasi-periodic oscillations (QPOs), the ratio of the two frequencies is 3:2. This supports the suggestion that double-peak kHz QPOs are due to a non-linear resonance between two modes of accretion disk oscillations. For the microquasars with known mass, we briefly compare the black hole spin estimates based on the orbital resonance model with the recently reported spin predictions obtained by fitting the spectral continua. Results of these two approaches are not in good agreement. We stress that if the spectral fit estimates are accurate and can be taken as referential (which is still questionable), the disagreement between the predicted and referential values would represent a rather generic problem for any relativistic QPO model, as no spin influence would appear in the observed 1/M scaling of the QPO frequencies. The epicyclic frequencies relevant in these models are often considered to be equal to those of a test particle motion. However modifications of the frequencies due to disc pressure or other non-geodesic effects may play an important role, and the inaccuracy introduced in the spin estimates by the test particle approximation could be crucial.
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    Non-linear resonance model of hi-frequency quasiperiodic oscillations (QPO) in X-ray sources: theory vs. observation

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    There is an impressive agreement between theoretical prediction of the high frequency twin peak QPO resonance model and the black-hole as well as neutron-star observational data. The model explains QPOs as two modes of accretion disk oscillations that are weakly coupled, non linear and resonant. It predicts that there should be 1/ mass scalling of frequencies, that the two frequencies ν_high, ν_low should be nearly linearly correlated for one source, ν_high = A ν_low + B, that the A, B coefficients should be anti correlated in a sample of neutron star sources, and that the difference of amplitudes in the two modes should vanish close to the resonance. All these predictions are confirmed by observations. No any other QPO model is able to explain all these observations.
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    LNRF-velocity hump-induced oscillations of a Keplerian disc orbiting near-extreme Kerr black hole: a possible explanation of high-frequency QPOs in GRS 1915+105

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    Context: At least four high-frequency quasiperiodic oscillations (QPOs) at frequencies 41 Hz, 67 Hz, 113 Hz, and 167 Hz were reported in a binary system GRS 1915+105 hosting near-extreme Kerr black hole with a dimensionless spin a > 0.98. Aims: We attempt to explain all four observed frequencies by an extension of the standard resonant model of epicyclic oscillations. Methods: We use the idea of oscillations induced by the hump of the orbital velocity profile (related to locally non-rotating frames-LNRF) in discs orbiting near-extreme Kerr black holes, which are characterized by a “humpy frequency” ν_h, that could excite the radial and vertical epicyclic oscillations with frequencies ν_r, ν_v. Due to non-linear resonant phenomena, the combinational frequencies are allowed as well. Results: Assuming mass M = 14.8 M⊙ and spin a = 0.9998 for the GRS 1915+105 Kerr black hole, the model predicts frequencies νh = 41 Hz, νr = 67 Hz, ν_h+νr = 108 Hz, and ν_v-νr = 170 Hz corresponding quite well to the observed ones. Conclusions: For black-hole parameters being in good agreement with those given observationally, the forced resonant phenomena in non-linear oscillations, excited by the “hump-induced” oscillations in a Keplerian disc, can explain high-frequency QPOs in near-extreme Kerr black-hole binary system GRS 1915+105 within the range of observational errors.
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    QPOs in Microquasars: the Spin Problem

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    In Galactic microquasars with double-peak kHz quasi-periodic oscillations (QPOs), the ratio of the two frequencies is 3:2. This supports the suggestion that double-peak kHz QPOs are due to a non-linear resonance between two modes of accretion disk oscillations. For the microquasars with known mass, we briefly compare the black hole spin estimates based on the orbital resonance model with the recently reported spin predictions obtained by fitting the spectral continua. Results of these two approaches are not in good agreement. We stress that if the spectral fit estimates are accurate and can be taken as referential (which is still questionable), the disagreement between the predicted and referential values would represent a rather generic problem for any relativistic QPO model, as no spin influence would appear in the observed 1/M scaling of the QPO frequencies. The epicyclic frequencies relevant in these models are often considered to be equal to those of a test particle motion. However modifications of the frequencies due to disc pressure or other non-geodesic effects may play an important role, and the inaccuracy introduced in the spin estimates by the test particle approximation could be crucial.
    Read More

    Non-linear resonance model of hi-frequency quasiperiodic oscillations (QPO) in X-ray sources: theory vs. observation

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    There is an impressive agreement between theoretical prediction of the high frequency twin peak QPO resonance model and the black-hole as well as neutron-star observational data. The model explains QPOs as two modes of accretion disk oscillations that are weakly coupled, non linear and resonant. It predicts that there should be 1/ mass scalling of frequencies, that the two frequencies ν_high, ν_low should be nearly linearly correlated for one source, ν_high = A ν_low + B, that the A, B coefficients should be anti correlated in a sample of neutron star sources, and that the difference of amplitudes in the two modes should vanish close to the resonance. All these predictions are confirmed by observations. No any other QPO model is able to explain all these observations.
    Read More

    LNRF-velocity hump-induced oscillations of a Keplerian disc orbiting near-extreme Kerr black hole: a possible explanation of high-frequency QPOs in GRS 1915+105

    by Zdeněk Stuchlík· 01 srpna, 2007· in Fyzika· 0 comments
    Context: At least four high-frequency quasiperiodic oscillations (QPOs) at frequencies 41 Hz, 67 Hz, 113 Hz, and 167 Hz were reported in a binary system GRS 1915+105 hosting near-extreme Kerr black hole with a dimensionless spin a > 0.98.
    Aims: We attempt to explain all four observed frequencies by an extension of the standard resonant model of epicyclic oscillations.
    Methods: We use the idea of oscillations induced by the hump of the orbital velocity profile (related to locally non-rotating frames-LNRF) in discs orbiting near-extreme Kerr black holes, which are characterized by a “humpy frequency” ν_h, that could excite the radial and vertical epicyclic oscillations with frequencies ν_r, ν_v. Due to non-linear resonant phenomena, the combinational frequencies are allowed as well.
    Results: Assuming mass M = 14.8 M⊙ and spin a = 0.9998 for the GRS 1915+105 Kerr black hole, the model predicts frequencies νh = 41 Hz, νr = 67 Hz, ν_h+νr = 108 Hz, and ν_v-νr = 170 Hz corresponding quite well to the observed ones.
    Conclusions: For black-hole parameters being in good agreement with those given observationally, the forced resonant phenomena in non-linear oscillations, excited by the “hump-induced” oscillations in a Keplerian disc, can explain high-frequency QPOs in near-extreme Kerr black-hole binary system GRS 1915+105 within the range of observational errors.
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    On a multi-resonant origin of high frequency QPOs in the atoll source 4U 1636-53

    by Zdeněk Stuchlík· 01 června, 2007· in Fyzika· 0 comments

    On a multi-resonant origin of high frequency QPOs in the atoll source 4U 1636-53

    by Zdeněk Stuchlík· 01 června, 2007· in Fyzika· 0 comments
    Publication date: Jun 2007 Abstract: Authors: Török, G.; Bakala, P.; Stuchlik, Z.; Šrámková, E.; https://ui.adsabs.harvard.edu/abs/2007xnnd.confP..10T
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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
    Change of sign of the LNRF-velocity radial gradient has been found for accretion discs orbiting a rapidly rotating Kerr black hole with spin a > 0.9953 (Keplerian discs) and a > 0.99979 (marginally stable thick discs). The maximal positive rate of change of the orbital velocity in terms of the proper radial distance introduces a locally defined critical frequency characterizing any processes in the disc capable to excite possible oscillations connected with the velocity hump. Comparing the "humpy frequency" related to distant observers with the epicyclic frequencies, we shall show that in Keplerian discs orbiting extremely rapid Kerr holes (1-a < 10-4) the ratio of the epicyclic frequencies and the humpy frequency is constant, i.e., independent of spin, being ˜3:2 for the radial epicyclic frequency and ˜11:2 for the vertical epicyclic frequency. For black holes with a ≈ 0.996, i.e., when the resonant phenomena with ratio 3:1 between the vertical and radial epicyclic oscillations occur near the radius of the critical humpy frequency, there is ratio of the radial epicyclic and the humpy frequency ˜1:12, i.e., the critical frequency is close to the low-frequency QPOs related to the high-frequency QPOs in such spacetimes. For a > 0.996 the resonant orbit with the ratio 4:1 between the vertical and radial epicyclic oscillations occurs in the region of the hump. In the case of thick discs, the situation is more complex due to the dependence on the distribution of the specific angular momentum L characterizing the disc rotation. For L = const tori and (1-a) < 10-6 the frequency ratios of the humpy frequency and the epicyclic frequencies are again constant and independent of both the spin and the specific angular momentum.
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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
    Properties of equipotential surfaces in test perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes will be summarized. The last closed surface crosses itself in the cusp(s) enabling outflow(s) of matter from the torus. The repulsive (positive) cosmological constant is responsible for the existence of the outer cusp (with a stabilizing effect on the tori because of the excretion) and strong collimation of open equipotential surfaces along the rotational axis. We shall present the mass estimates for tori with an adiabatic equation of state enabling to put limits on their central mass density, for which the approximation of test fluid is adequate.
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