Publication date: Jun 2015
Abstract:
The Resonant Switch (RS) model of twin high-frequency quasi-periodic
oscillations (HF QPOs) observed in neutron star binary systems, based on
switch of the twin oscillations at a resonant point, has been applied to
the atoll source 4U 1636-53 under assumption that the neutron star
exterior can be approximated by the Kerr geometry. Strong restrictions
of the neutron star parameters M (mass) and a (spin) arise due to
fitting the frequency pairs admitted by the RS model to the observed
data in the regions related to the resonant points. The most precise
variants of the RS model are those combining the relativistic precession
frequency relations with their modifications. Here, the neutron star
mass and spin estimates given by the RS model are confronted with a
variety of equations of state (EoS) governing structure of neutron stars
in the framework of the Hartle-Thorne theory of rotating neutron stars
applied for the observationally given rotation frequency
frot≍580 Hz (or alternatively frot≍290
Hz) of the neutron star in 4U 1636-53. It is shown that only two
variants of the RS model based on the Kerr approximation are compatible
with two EoS applied in the Hartle-Thorne theory for
frot≍580 Hz, while no variant of the RS model is
compatible for frot≍290 Hz. The two compatible variants
of the RS model are those giving the best fits of the observational
data. However, a self-consistency test by fitting the observational data
to the RS model with oscillation frequencies governed by the
Hartle-Thorne geometry described by three spacetime parameters M,a and
(quadrupole moment) q related by the two available EoS puts strong
restrictions. The test admits only one variant of the RS model of twin
HF QPOs for the Hartle-Thorne theory with the EoS predicting the
parameters of the neutron star M≍2.10 M⊙,
a≍0.208, and q/a2≍1.77.
Authors:
Stuchlìk, Z.; Urbanec, M.; Kotrlovà, A.; Török, G.; Goluchovà, K.;