**Publication date:** Mar 2014

**Abstract:**

Resonant Switch (RS) model has recently been proposed as an alternative

to the standard models of twin-peak high-frequency quasi-periodic

oscillations (HF QPOs) observed in low-mass X-ray binaries containing a

neutron star. The model assumes switch of twin oscillations at a

resonant point, where frequencies of the upper and lower oscillations

ν_{U} and ν_{L} become commensurable and one pair of the

oscillating modes (corresponding to a specific model of HF QPOs) changes

to some other pair due to non-linear resonant phenomena. We test the RS

model for the atoll source 4U 1636-53, where we assume two resonant

points observed at frequency ratios ν_{U}:ν_{L}=3:2,

5:4, by fitting the pairs of the oscillatory modes to the observed data

in the regions related to the resonant points. Among acceptable variants

of the RS model the most promising are those combining the relativistic

precession (RP) and the total precession (TP) frequency relations or

their modifications. The precision of the fits is shown to be strongly

increased in comparison to fits realized by individual pairs along the

whole data range. We demonstrate that the χ^{2} test is

significantly improved. Fitting of the HF QPO data in the source 4U

1636-53 by the RP1-RP variant of the RS model gives the best results and

implies that the neutron star mass and dimensionless spin are M≍2.2

M_{sun} and a≍0.27.

**Authors:**

Stuchlik, Z.; Kotrlova, A.; Torok, G.; Goluchova, K.;