**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

νU and νL 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

νU:νL=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 χ2 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 Msun

and a≍0.27.

**Authors:**

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