The iron Kα-line as a tool for an evaluation of black hole parameters

Zakharov, A. F.

doi:10.1063/1.1843523

Cited by 5 publications

(4 citation statements)

References 57 publications

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“…In fact, the black hole parameter estimates come from a variety of astrophysical observations [41,42,51,60,61,50]. The black hole spin estimates are commonly given by the optical methods, namely by X-ray line profiles [48,36,26,28,86,87] and X-ray continuum spectra [52,53,66], and by quasiperiodic oscillations, the frequency of which enable, in principle, the most precise spin estimates, because of high precision of the frequency measurements. 2 Therefore, we discuss here in detail the orbital resonance model of QPOs, which seems to be the most promising in explaining the observational data from four microquasars, namely GRO J1655-40, XTE 1550-564, H 1743-322, GRS 1915+105 [80,76,77,75] and in Sgr A * [11,13,76], or some extragalactic sources as NGC 5408 X-1 [70].…”

Section: Introductionmentioning

confidence: 99%

Orbital resonances in discs around braneworld Kerr black holes

2008

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Rotating black holes in the brany universe of the Randall-Sundrum type are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b<0 rotating black holes with dimensionless spin a>1 are allowed. We investigate the role of the tidal charge b in the orbital resonance model of QPOs in black hole systems. The orbital Keplerian, the radial and vertical epicyclic frequencies of the equatorial, quasicircular geodetical motion are given and their radial profiles are discussed. The resonant conditions are given in three astrophysically relevant situations: for direct (parametric) resonances, for the relativistic precession model, and for some trapped oscillations of the warped discs, with resonant combinational frequencies. It is shown, how b could influence matching of the observational data indicating the 3:2 frequency ratio observed in GRS 1915+105 microquasar with prediction of the orbital resonance model; limits on allowed range of the black hole parameters a and b are established. The "magic" dimensionless black hole spin enabling presence of strong resonant phenomena at the radius where \nu_K:\nu_{\theta}:\nu_r=3:2:1 is determined in dependence on b. Such strong resonances could be relevant even in sources with highly scattered resonant frequencies, as those expected in Sgr A*. The specific values of a and b are given also for existence of specific radius where \nu_K:\nu_{\theta}:\nu_r=s:t:u with 5>=s>t>u being small natural numbers. It is shown that for some ratios such situation is impossible in the field of black holes. We can conclude that analysing the microquasars high-frequency QPOs in the framework of orbital resonance models, we can put relevant limits on the tidal charge of brany Kerr black holes.Comment: 31 pages, 19 figures, to appear in General Relativity and Gravitatio

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Section: Introductionmentioning

confidence: 99%

Orbital resonances in discs around braneworld Kerr black holes

2008

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“…The spin estimates with a ∼ 1 are implied by the Xray observations of AGN as MCG-6-30-15 [52] or the GBHC GRS 1915+105 [53] and are related to a variety of optical phenomena that deserve attention. Among them the most important seem to be the spectral continuum [51][52][53][54][55][56], spectral line profiles [57][58][59][60][61][62][63][64][65][66][67][68][69][70], and quasiperiodic oscillations explained by the orbital resonant models applied to near-extreme black holes [12,[71][72][73][74][75][76][77]. All such objects seem to be possible candidates for the Kerr superspinars and deserve attention and detailed study of data.…”

Section: Observational Signatures Of Kerr Superspinarsmentioning

confidence: 99%

Evolution of Kerr superspinars due to accretion counterrotating thin discs

Stuchlík

Hledík

Truparova

2011

Class. Quantum Grav.

106

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String theory predicts the existence of extremely compact objects spinning faster than Kerr black holes. The spacetime exterior to such superspinars is described by Kerr naked singularity geometry breaking the black-hole limit on the internal angular momentum. We demonstrate that the conversion of Kerr superspinars into a near-extreme black hole due to an accretion counterrotating Keplerian disc is much more effective in comparison with the case of a corotating one since both the accreted rest mass necessary for conversion and the evolution time of conversion are by orders smaller for counterrotating discs. The conversion time of Kerr superspinars is given for several accretion regimes, and it is shown that the self-regulated accretion flow implies fastest evolution to the black-hole state. In the final stages of the conversion, Kerr superspinars can serve as very efficient particle accelerators in the region where the black-hole horizon forms.

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“…Based on our previous results [32,33], we write our own ray-shooting code to check conclusions about the interpretation of observational data in the framework of the theoretical model. We solved several relevant astrophysical problems with our code [34,35,36,37,38,39,40,41,42,43,44], in particular, we generalize Matt et al's result [26] about the existence of extra peaks in relativistic line shapes for the case of a Kerr black hole if a distant observer is located near the equatorial plane [45] (initially Matt et al [26] established their result for a Schwarzschild black hole case) while in [46] we showed that in principle one could constrain a magnetic field, when the magnetic field is strong enough. One can find more recent reviews on theoretical aspects of relativistic line shapes in [47,48].…”

Section: Centennial History Of Black Holes In Briefmentioning

confidence: 99%

The black hole at the Galactic Center: Observations and models

Zakharov

2018

Int. J. Mod. Phys. D

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One of the most interesting astronomical objects is the Galactic Center. It is a subject of intensive astronomical observations in different spectral bands in recent years. We concentrate our discussion on a theoretical analysis of observational data of bright stars in the IR-band obtained with large telescopes. We also discuss the importance of VLBI observations of bright structures which could characterize the shadow at the Galactic Center. If we adopt general relativity (GR), there are a number of theoretical models for the Galactic Center, such as a cluster of neutron stars, boson stars, neutrino balls, etc. Some of these models were rejected or the range of their parameters is significantly constrained with consequent observations and theoretical analysis. In recent years, a number of alternative theories of gravity have been proposed because there are dark matter (DM) and dark energy (DE) problems. An alternative theory of gravity may be considered as one possible solution for such problems. Some of these theories have black hole solutions, while other theories have no such solutions. There are attempts to describe the Galactic Center with alternative theories of gravity and in this case one can constrain parameters of such theories with observational data for the Galactic Center. In particular, theories of massive gravity are intensively developing and theorists have overcome pathologies presented in the initial versions of these theories. In theories of massive gravity, a graviton is massive in contrast with GR where a graviton is massless. Now these theories are considered as an alternative to GR. For example, the LIGO–Virgo collaboration obtained the graviton mass constraint of about [Formula: see text] eV in their first publication about the discovery of the first gravitational wave detection event that resulted of the merger of two massive black holes. Surprisingly, one could obtain a consistent and comparable constraint of graviton mass at a level around [Formula: see text][Formula: see text]eV from the analysis of observational data on the trajectory of the star S2 near the Galactic Center. Therefore, observations of bright stars with existing and forthcoming telescopes such as the European extremely large telescope (E-ELT) and the thirty meter telescope (TMT) are extremely useful for investigating the structure of the Galactic Center in the framework of GR, but these observations also give a tool to confirm, rule out or constrain alternative theories of gravity. As we noted earlier, VLBI observations with current and forthcoming global networks (like the Event Horizon Telescope) are used to check the hypothesis about the presence of a supermassive black hole at the Galactic Center.

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The iron Kα-line as a tool for an evaluation of black hole parameters

Cited by 5 publications

References 57 publications

Orbital resonances in discs around braneworld Kerr black holes

Orbital resonances in discs around braneworld Kerr black holes

Evolution of Kerr superspinars due to accretion counterrotating thin discs

The black hole at the Galactic Center: Observations and models

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