Interpretation of ∼35 Hz QPO in the atoll source 4U 1702-42 as a low branch of the Keplerian oscillations under the influence of the Coriolis force

The recent model of quasi-periodic oscillations in neutron star binaries has suggested the existence of two branches of QPOs due to the influence of Coriolis force on the linear Keplerian oscillator: one branch with frequencies similar to 400-1200 Hz and another branch with frequencies an order of magnitude lower. The frequencies of the high branch nu(h) hold a hybrid frequency relation with the Keplerian frequency nu(K): nu(h)(2) = nu(K)(2) + Omega(2)/pi(2), where Omega is the rotational frequency of the star's magnetosphere. The frequency of the low branch is nu(L) = (Omega/pi)(nu(K)/nu(h)) sin delta, where delta is a small angle between Omega and the vector normal to the plane of Keplerian oscillations. The observations of the source 4U 1702-42 have shown that the centroid of the similar to 35 Hz QPO tracks the frequency of the kilohertz oscillations. We interpret the similar to 35 Hz oscillations as nu(L) and find delta = 3.degrees 9 +/- 0.degrees 2. Our results make 4U 1702-42 the second source (after Sco X-1) for which the theoretically derived lower branch is identified (within our model) and delta is calculated. The inferred angle delta stays approximately the same over the significant range of nu(K) (650-900 Hz), as expected from the model. Based on our model, we present a classification of QPO frequencies in the source 4U 1702-42 observed above and below nu(L).