**Publication date:** Dec 2012

**Abstract:**

Resonant Switch (RS) model of twin peak high-frequency quasi-periodic

oscillations (HF QPOs) 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 the twin

oscillations change from one pair of the oscillating modes

(corresponding to a specific model of HF QPOs) to some other pair due to

non-linear resonant phenomena. The RS model is used to determine range

of allowed values of spin a and mass M of the neutron star located in

the atoll source 4U 1636-53 where two resonant points are observed at

frequency ratios ν_{U}:ν_{L}=3:2, 5:4. We consider the

standard specific models of the twin oscillations based on the orbital

and epicyclic geodetical frequencies. The resonant points are determined

by the energy switch effect exhibited by the vanishing of the amplitude

difference of the upper and lower oscillations. The predicted ranges of

the neutron star parameters are strongly dependent on the twin modes

applied in the RS model. We demonstrate that for some of the oscillatory

modes used in the RS model the predicted parameters of the neutron star

are unacceptable. Among acceptable RS models the most promising are

those combining the Relativistic Precession and the Total Precession

frequency relations or their modifications.

**Authors:**

Stuchlík, Z.; Kotrlová, A.; Török, G.;