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.;