Publication date: Dec 2007
Abstract:
The kHz quasiperiodic oscillations (QPOs) observed in low-mass X-ray
neutron star binaries are most likely connected to the orbital motion in
the accretion disc and show datapoint clustering of frequency ratio
between the upper and lower QPOs in small natural numbers. It is shown
for the atoll source 4U 1636-53 that using the Hartle-Thorne metric to
describe the neutron star spacetime, the data clustered around the
frequency ratios 3/2 and 5/4 could be fitted by three models
(Relativistic Precession, Vertical Precession and Total Precession)
involving the hot spot orbital motion with Keplerian, radial epicyclic
and vertical epicyclic frequencies. We demonstrate that with taking into
account the hotspots interaction with the neutron star magnetic field
the discussed three models can provide good fits implying reasonable
values of the neutron star mass and angular momentum. Therefore the
hypothesis of more instances of one orbital resonance has the potential
to explain the kHz QPO nature in the source 4U 1636-53.
Authors:
Török, Gabriel; Bakala, Pavel; Stuchlík, Zdeněk; Šrámková, Eva;