
Energy balance of corona in blackhole accretion disks
Tynianskaia, Valeriia ; Bursa, Michal (advisor) ; Svoboda, Jiří (referee)
The presence of Xray 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 (lamppost 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


Numerical implementation of equations for photon motion in Kerr spacetime
Bursa, Michal
Raytracing is one of the essential tools for accurate modeling of spectra and variability of various astrophysical objects. It has a major importance in relativisticenvironments, where light endures to a number of relativistic effects. Because the trajectories of light rays in curved spacetimes, and in Kerr spacetime in particular, are highly nontrivial, we summarize the equations governing the motion of photon\n(or any other zero rest mass particle) and give analytic solution of the equations thatcan be further used in practical computer implementations.

 
 
 
 
 

Modulace HFQPO
Bursa, Michal
We study stronggravity effects on modulation of radiation emerging from accreting compact objects as a possible mechanism for flux modulation in QPOs.


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 Xray binaries. In this note we report on recent analysis of occurrences and properties of kHz QPOs in the source 4U163653. 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.

 