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Polarisation properties of X-ray emission from accreting supermassive black holes
Podgorný, Jakub ; Dovčiak, Michal (advisor) ; Done, Christine (referee) ; Porquet, Delphine (referee)
This dissertation elaborates on X-ray polarization features of astrophysical environ- ments near accreting black holes. Although the work was originally assigned to su- permassive black holes in active galactic nuclei, the results are also largely applicable to stellar-mass black holes in X-ray binary systems. Several numerical models predicting the X-ray polarization from these sources are presented, including their immediate ap- plications in the interpretation of the latest discoveries achieved thanks to the Imaging X-ray Polarimetry Explorer (IXPE) mission that began operating in December 2021. The modeling ranges from radiative transfer effects in atmospheres of accretion discs to general-relativistic signatures of X-rays travelling in vacuum near the central black holes to reprocessing events in distant, circumnuclear components. Various scales in phys- ical and computational complexity are examined. A unifying element of this dissertation is the focus on reflection of X-rays from partially ionized matter. 1
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Gravitational Lensing by Substructures in Dark Matter Halos
Karamazov, Michal ; Heyrovský, David (advisor) ; Bartelmann, Matthias (referee) ; Dovčiak, Michal (referee)
Gravitational lensing serves as an invaluable tool for studying the distribution of mat- ter in the universe. This matter is predominantly dark and clumped into centrally concen- trated hierarchically structured halos of galaxies and galaxy clusters. Early comparisons suggested discrepancies between the high population of substructures predicted by cos- mological simulations and the lack of corresponding observational data. More recently, a major discrepancy in the opposite sense was reported from analyses of lensing galaxy clusters: the lensing efficiency of their substructures was found to be much higher than predictions based on cosmological simulations. In this thesis, we examine gravitational lensing by substructures embedded in dark-matter halos with Navarro-Frenk-White (NFW) density profiles. We start by a detailed investigation of a simple model with a single point mass perturbing the halo. Using analytical methods, we study its critical curves, caustics and their transitions. Next, we explore the geometry of lensed images and the weak-lensing characteristics of the same simple model, developing novel ways of their visualization. Finally, we construct a more realistic lens model of a galaxy cluster con- sisting of an ellipsoidal cluster halo combined with a population of truncated ellipsoidal galaxy...
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Resolving stellar surfaces with binary gravitational microlensing
Pejcha, Ondřej ; Heyrovský, David (advisor) ; Dovčiak, Michal (referee)
Binary gravitational microlensing has demonstrated excellent prospects for studying the surface brightness distribution of stars. In this work we study the extended-source eects that aect the amplication of the source ux. We identify regions in the geometry that are sensitive to the extended source and nd previously unknown areas between facing cusps of multi-part caustics. We nd out that the probability of detecting the extended-source eect can be as much as two times higher than the probability of observing pure caustic crossing. We explore the chromaticity of binary microlensing and compare two classes of models of limb darkening. We describe spectral changes during binary microlensing and compare their amplitude to the point-lens case. Finally, we investigate the linear fold approximation and nd signicant residuals even in cases favorable for the method.
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Gravitational microlensing by a few-body system
Daněk, Kamil ; Heyrovský, David (advisor) ; Dovčiak, Michal (referee)
In the present work we study gravitational microlenses consisting of a few point masses. We present the theoretical framework of n-point-mass lensing, and followup by a more detailed description of binary and triple lenses. We demonstrate the analysis of critical curves and caustics of the bojary lens and apply the same approach to the case of triple lenses. We divided several two-dimensional cuts of the parameter space into areas with different topology of critical curves. We studied the amplification of a source located in the vicinity of interesting parts of the caustic. We tested the applicability of an approximation for the amplification at the intersection of two folds. Finally, we applied the formalism to the case of the observed triple-lens microlensing event OGLE-2006-BLG-109.
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Measuring accretion disk properties from quasar microlensing
Ledvina, Lukáš ; Heyrovský, David (advisor) ; Dovčiak, Michal (referee)
When we observe a~distant quasar through an intervening galaxy we may see a~number of observable images caused by hte deflecton of light in galaxy's gravitational field. If an image passes through the stellar population of the galaxyit can be additionally microlensed by individual stars. In this work we first compute microlensing magnification maps for a~point source. We than use these maps to determine light curves for extended source, namely for a~quasar accretion disc.In the second part we compare obtained light curves for different discs and we will study the influence of inclination, orientation and surface brightness distribution of an accretion disk on the light curve during an individual crossing of a~cusp and fold of microlensing custic network
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Polarisation of X-ray emission from accretion discs in active galactic nuclei
Podgorný, Jakub ; Dovčiak, Michal (advisor) ; Marin, Frédéric (referee)
The presented thesis deals with theoretical modeling of the X-ray emission from active galactic nuclei. It studies spectral and polarisation properties of local radiation reflected from the surrounding accretion disc, which is being illuminated by a hot corona above, as well as global observational perspectives at infinity for unobscured radio-quiet sources. Modeling of this kind could then serve for observational fitting of spin of the central supermassive black hole, constraining the accretion disc's or coronal properties, or de- termining observer's inclination towards the systems. A radiative transfer Monte Carlo simulation code STOKES [Goosmann and Gaskell, 2007, Marin et al., 2012, 2015, Marin, 2018] is used for local computations. Its performance is compared to results of other attempts already existing in literature and analytical approximations. The local scheme is discussed mostly in terms of emergent polarisation that has been for the first time simulated for these types of objects with high accuracy. Integration over the accretion disc and superposition with the primary radiation in the so-called lamp-post or extended coronal model, including all general relativistic effects in the vicinity of the central super- massive black hole, is then performed on the basis of already existing routine...
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Polarisation of X-ray emission from accretion discs in active galactic nuclei
Podgorný, Jakub ; Dovčiak, Michal (advisor)
The presented thesis deals with theoretical modeling of the X-ray emission from active galactic nuclei. It studies spectral and polarisation properties of local radiation reflected from the surrounding accretion disc, which is being illuminated by a hot corona above, as well as global observational perspectives at infinity for unobscured radio-quiet sources. Modeling of this kind could then serve for observational fitting of spin of the central supermassive black hole, constraining the accretion disc's or coronal properties, or de- termining observer's inclination towards the systems. A radiative transfer Monte Carlo simulation code STOKES [Goosmann and Gaskell, 2007, Marin et al., 2012, 2015, Marin, 2018] is used for local computations. Its performance is compared to results of other attempts already existing in literature and analytical approximations. The local scheme is discussed mostly in terms of emergent polarisation that has been for the first time simulated for these types of objects with high accuracy. Integration over the accretion disc and superposition with the primary radiation in the so-called lamp-post or extended coronal model, including all general relativistic effects in the vicinity of the central super- massive black hole, is then performed on the basis of already existing routine...
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Understanding the iron K alpha line emissivity profile with GR radiative transfer code
Zhang, Wenda ; Dovčiak, Michal ; Bursa, Michal ; Svoboda, Jiří ; Karas, Vladimír
In this work, we present calculations of the illumination and the iron K alpha emissivity profiles performed with the GR radiative transfer code Monk that employs the Monte Carlo method. In most previous studies the distinction between the illumination and emissivity profiles was not clearly made. For AGN discs, the emissivity profile has a similar shape with the illumination profile, but in the inner most region the former is steeper than the latter, where as for accretion discs in black hole X-ray binaries, the distinction between the two profiles is more dramatic. We find out that the different behavior between AGN and black hole X-ray binary discs is due to the different energy spectra of the illuminating radiation. This suggests that the emissivity profile of the iron Kαline cannot be determined by black hole spin and corona geometry alone and the energy spectrum of the illuminating radiation has to be taken into account. We also study the dependence of the emissivity profile on the geometry of the corona.
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Polarisation of X-ray emission from accretion discs in active galactic nuclei
Podgorný, Jakub ; Dovčiak, Michal (advisor) ; Marin, Frédéric (referee)
The presented thesis deals with theoretical modeling of the X-ray emission from active galactic nuclei. It studies spectral and polarisation properties of local radiation reflected from the surrounding accretion disc, which is being illuminated by a hot corona above, as well as global observational perspectives at infinity for unobscured radio-quiet sources. Modeling of this kind could then serve for observational fitting of spin of the central supermassive black hole, constraining the accretion disc's or coronal properties, or de- termining observer's inclination towards the systems. A radiative transfer Monte Carlo simulation code STOKES [Goosmann and Gaskell, 2007, Marin et al., 2012, 2015, Marin, 2018] is used for local computations. Its performance is compared to results of other attempts already existing in literature and analytical approximations. The local scheme is discussed mostly in terms of emergent polarisation that has been for the first time simulated for these types of objects with high accuracy. Integration over the accretion disc and superposition with the primary radiation in the so-called lamp-post or extended coronal model, including all general relativistic effects in the vicinity of the central super- massive black hole, is then performed on the basis of already existing routine...
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