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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.
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Confronting models of twin peak quasi-periodic oscillations: Mass and spin estimates fixed by neutron star equation of state
Török, G. ; Goluchová, K. ; Urbanec, M. ; Šrámková, E. ; Adámek, K. ; Urbancová, G. ; Pecháček, Tomáš ; Bakala, P. ; Stuchlík, Z. ; Horák, Jiří ; Juryšek, J.
In the work authors compare simplified calculations that assume Kerr background geometry to the detailed calculations considering NS oblateness influence in Hartle-Thorne spacetimes.
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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.
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