National Repository of Grey Literature 10 records found  Search took 0.01 seconds. 
Perturbing the accretion flow onto a supermassive black hole by a passing star
Suková, Petra ; Zajaček, M. ; Witzany, V. ; Karas, Vladimír
The close neighbourhood of a supermassive black hole contains not only accreting gas and dust, but also stellar-sized objects like stars, stellar-mass black holes, neutron stars, and dust-enshrouded objects that altogether form a dense nuclear star-cluster.These objects interact with the accreting medium and they perturb the otherwise quasi-stationary configuration of the accretion flow. We investigate how the passages of a star can influence the black hole gaseous environment with GRMHD 2D and3D simulations. We focus on the changes in the accretion rate and the associated emergence of outflowing blobs of plasma.
From gappy to ringed: signatures of an accretion disk radial structure in profiles of the reflection line
Štolc, Marcel ; Zajaček, M. ; Karas, Vladimír
We focus on the theoretical profiles of a spectral line produced by reflection of the surface of both gappy accretion disk and a ring-like structure near a black hole. We describe the relativistic effects in an approximative manner. While a smooth accretion disk leads to a typical, double-horn shape with unequal wings due to Doppler boosting and an additional peak due to the lensing amplification at high inclination angle, the gaps and rings give rise to a more complex dependence which reflects the location and the radial extent of the inhomogeneities in the accretion flow.
Energy balance of corona in black-hole accretion disks
Tynianskaia, Valeriia ; Bursa, Michal (advisor) ; Svoboda, Jiří (referee)
The presence of X-ray radiation that comes from the innermost regions of Active Galactic Nuclei indicates a presence of a hot gas component located close to the central black hole. The exact location and geometry of this so called corona is not known and various configurations are being considered in the literature. One of the suggestions for the geometry is a rather compact region located on the symmetry axis of the black hole (lamp-post model). Another variant is a layer that surrounds the accretion disk on both sides (slab model). Other models consider anything in between also in combination with a truncated disk. One of the key questions connected with the corona that is not often addressed is how is the corona energized, i.e. where does it take energy from. Assuming the disk is the only source of energy in an accreting system and that its internal energy is partly radiated and partly used to support magnetic fields, we evaluate geometrical constraints on the corona from the energy conservation condition. Lastly, we try to investigate the total emitted spectrum of a system consisting of a central black hole, a thin accretion disk and a slab corona. 1
A one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
Török, G. ; Goluchová, K. ; Šrámková, J. ; Horák, Jiří ; Bakala, P. ; Urbanec, M.
Timing analysis of X-ray flux in more than a dozen low-mass X-ray binary systems containing a neutron star reveals remarkable correlations between frequencies of two characteristic peaks present in the power-density spectra. We find a simple analytic relation that well reproduces all these individual correlations. We link this relation to a physical model which involves accretion rate modulation caused by an oscillating torus.
Epicyclic oscillations of thick relativistic disks
Horák, Jiří ; Straub, O. ; Šrámková, E. ; Goluchová, K. ; Török, G.
We study epicyclic oscillations of thick relativistic tori with constant specific angular momentum distribution using the finite element numerical method. We have compared frequencies of the axisymmetric and non-axisymmetric modes with the analytic formulae obtained by Straub and Šrámková (2009) and Fragile et al. (2016). We have found excellent agreement in the case of axisymmetric radial epicyclic modes. In the case of the axisymmetric vertical epicyclic modes and non-axisymmetric modes in general, the analytic approximation agrees with numerical results only for tori of moderate thicknesses. Our analysis also revealed an instability of the thick constant angular momentum tori with respect to the radial epicyclic oscillation.
On oscillations in turbulent accretion disks: I. A general approach
Horák, Jiří
In the article a general theory of a wave propagation in a turbulent media is reviewed.
Porovnání modelů relativistické čáry železa
Svoboda, Jiří ; Dovčiak, Michal ; Goosmann, René ; Karas, Vladimír
The analysis of the broad iron line profile in the X-ray spectra of active galactic nuclei and black hole X-ray binaries allows us to constrain the spin parameter of the black hole. We compare the constraints on the spin value for two X-ray sources, MCG-6-30-15 and GX 339-4, with a broad iron line using present relativistic line models in XSPEC - LAOR and KYRLINE.
O vzájemných vazbách mezi kHz QPOs
Török, G. ; Bursa, Michal ; Horák, Jiří ; Stuchlík, Z. ; Bakala, P.
We further investigate the issue of kHz QPO frequency ratios in neutron star low mass X-ray binaries. In this note we report on recent analysis of occurrences and properties of kHz QPOs in the source 4U1636-53. Assuming that kHz QPOs occur in pairs whose frequencies are linearly correlated, we find a prominent frequency range that separates upper and lower QPO observations.
Kinetický model kvasiperiodických oscilací plynných prstenců
Hadrava, Petr
In context of 3:2 resonant quasiperiodic oscillations, a method of "1+1/2 -dimensional" non-ideal gas dynamics is used to model axisymmetric oscillations of an orbiting ring. It is shown that the characteristic frequencies of the oscillations are influenced by the degree of freedom in the inner shear of the ring and by the rate of relaxation.
Formation of eccentric disks around black holes
Hadrava, Petr ; Řezáč, R. ; Oestgaard, E.
The formation and evolution of eccentric disks around black holes due to explosion of a companion on an eccetric orbit is modeled by means of exact general-relativistic N-particle treatment. It is shown that in spite of the generally accepted view that the debris must be quickly smeared out to a circular accretion disk.

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