Publication date: Dec 2014
Abstract:
Twin-peak quasiperiodic oscillations (QPOs) are observed in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. In our work we consider several QPO models and focus especially on the atoll source 4U 1636-53 with its large set of QPO measurements. We find that the considered models require the QPO excitation radii in 4U 1636-53 to be close to the inner-most stable circular orbit of the accretion disc. We explore and summarize mass-angular-momentum relations and limits on NS compactness implied by individual QPO models. We confront these relations with NS parameters given by various NS equations of state (EoS). The application of concrete EoS removes the degeneracy in the mass and angular momentum determined from the QPO models when the spin frequency is known. Moreover, the applied NS EoS are compatible only with some of the considered QPO models. In our work we compare simplified calculations that assume Kerr background geometry to the detailed calculations considering NS oblateness influence in Hartle-Thorne spacetimes.
Authors:
Török, Gabriel; Goluchová, Kateřina; Urbanec, Martin; Šrámková, Eva; Adámek, Karel; Urbancová, Gabriela; Pecháček, Tomáš; Bakala, Pavel; Stuchlík, Zdeněk; Horák, Jiří; Juryšek, Jakub;