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Quasar accretion disk mapping by gravitational microlensing
Ledvina, Lukáš ; Heyrovský, David (advisor) ; Horák, Jiří (referee)
Quasar microlensing is a relatively newly explored phenomenon, which is ideally suited for studying the spatial distribution of emission from the innermost accretion disc. By now we know many macrolensed quasars, in which we can observe multiple images formed by the deflection of light in the gravitational field of an intervening galaxy. In case one of these images passes directly through the stellar population of the galaxy, it can be additionally microlensed by individual stars. The gravitational field of these stars forms a caustic network for light passing by. When a quasar accretion disc crosses behind this network, induced changes can be observed in the light curve as well as in the spectrum. In the first part of this thesis we study the statistics of the time intervals between successive caustic crossings. In the second part we use a fully relativistic Kerr-metric thin-disc model for studying the light curve of a fold-caustic crossing and its dependence on the accretion- disc parameters. In the last part we simulate changes in the X-ray iron-line profile during a fold-caustic crossing. We find characteristic spectral features formed on the line, and derive their analytical description. Finally, we map the maximum strength of microlensing-generated peaks on the spectral line for different...
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Quasar accretion disk mapping by gravitational microlensing
Ledvina, Lukáš ; Heyrovský, David (advisor)
Quasar microlensing is a relatively newly explored phenomenon, which is ideally suited for studying the spatial distribution of emission from the innermost accretion disc. By now we know many macrolensed quasars, in which we can observe multiple images formed by the deflection of light in the gravitational field of an intervening galaxy. In case one of these images passes directly through the stellar population of the galaxy, it can be additionally microlensed by individual stars. The gravitational field of these stars forms a caustic network for light passing by. When a quasar accretion disc crosses behind this network, induced changes can be observed in the light curve as well as in the spectrum. In the first part of this thesis we study the statistics of the time intervals between successive caustic crossings. In the second part we use a fully relativistic Kerr-metric thin-disc model for studying the light curve of a fold-caustic crossing and its dependence on the accretion- disc parameters. In the last part we simulate changes in the X-ray iron-line profile during a fold-caustic crossing. We find characteristic spectral features formed on the line, and derive their analytical description. Finally, we map the maximum strength of microlensing-generated peaks on the spectral line for different...
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Quasar accretion disk mapping by gravitational microlensing
Ledvina, Lukáš ; Heyrovský, David (advisor)
Quasar microlensing is a relatively newly explored phenomenon, which is ideally suited for studying the spatial distribution of emission from the innermost accretion disc. By now we know many macrolensed quasars, in which we can observe multiple images formed by the deflection of light in the gravitational field of an intervening galaxy. In case one of these images passes directly through the stellar population of the galaxy, it can be additionally microlensed by individual stars. The gravitational field of these stars forms a caustic network for light passing by. When a quasar accretion disc crosses behind this network, induced changes can be observed in the light curve as well as in the spectrum. In the first part of this thesis we study the statistics of the time intervals between successive caustic crossings. In the second part we use a fully relativistic Kerr-metric thin-disc model for studying the light curve of a fold-caustic crossing and its dependence on the accretion- disc parameters. In the last part we simulate changes in the X-ray iron-line profile during a fold-caustic crossing. We find characteristic spectral features formed on the line, and derive their analytical description. Finally, we map the maximum strength of microlensing-generated peaks on the spectral line for different...
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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
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Fields of current loops around black holes
Vlasáková, Zuzana ; Semerák, Oldřich (advisor) ; Svítek, Otakar (referee)
The magnetic field of a test circular current loop placed symmetrically around a Schwarzschild black hole has been determined several times in the literature and solutions has been expressed by different formulas. We compare these formulas analytically as well as numerically, and show, in particular, how they behave on the symmetry axis, in the equatorial plane and on the horizon. The problem is relevant for modelling accretion discs around black holes.
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Chaos in deformed black-hole fields
Witzany, Vojtěch ; Semerák, Oldřich (advisor) ; Kopáček, Ondřej (referee)
The consequences of two key approximations of accretion-disc physics near black holes are studied in this thesis. First, the question of effective ``pseudo-Newtonian" potentials mimicking a black hole is investigated both through numerical simulations and analytical means, and second, the neglect of additional gravitating matter near accreted-upon black holes and its consequences are put to test. After some broader discussion of integrability, resonance and chaos, a general "pseudo-Newtonian" limit for geodesic motion is derived, and applied for the case of null geodesics near a glowing toroid and for time-like geodesics in the Kerr metric. Afterwards, a new Newtonian gravitational potential for non- singular toroids is proposed and its usefulness for the so-called Weyl space-times is discussed. Finally, a new pseudo-Newtonian potential is introduced and applied alongside already known potentials in models of free test particle motion in the field of a black hole with a disc or ring, in complete analogy with previous exact-relativistic studies, and the previous conclusion of chaos in disc/ring-hole models is confirmed. Overall, the pseudo-Newtonian framework is able to reproduce a number of key features of the original systems with notable differences arising only as a consequence of extremely strong or...
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Quasar accretion disk mapping by gravitational microlensing
Ledvina, Lukáš ; Heyrovský, David (advisor) ; Horák, Jiří (referee)
Quasar microlensing is a relatively newly explored phenomenon, which is ideally suited for studying the spatial distribution of emission from the innermost accretion disc. By now we know many macrolensed quasars, in which we can observe multiple images formed by the deflection of light in the gravitational field of an intervening galaxy. In case one of these images passes directly through the stellar population of the galaxy, it can be additionally microlensed by individual stars. The gravitational field of these stars forms a caustic network for light passing by. When a quasar accretion disc crosses behind this network, induced changes can be observed in the light curve as well as in the spectrum. In the first part of this thesis we study the statistics of the time intervals between successive caustic crossings. In the second part we use a fully relativistic Kerr-metric thin-disc model for studying the light curve of a fold-caustic crossing and its dependence on the accretion- disc parameters. In the last part we simulate changes in the X-ray iron-line profile during a fold-caustic crossing. We find characteristic spectral features formed on the line, and derive their analytical description. Finally, we map the maximum strength of microlensing-generated peaks on the spectral line for different...
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Magnetic fields of current loops around black holes
Pejcha, Jakub ; Semerák, Oldřich (advisor) ; Ledvinka, Tomáš (referee)
Magnetic field of equatorial current loop around Schwarzschild (or Kerr) black hole has been studied in many papers and solutions expressed in different forms. In this work we summarize derivations of some of these solutions, illustrate them on specific examples and compare these examples. We also indicate analytic com- parison of some of the formulas. Published formulas lead, as expected, to same results, but some of them are more convenient for numerical evaluation. 1
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