1999ApJ...523L..73O

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 ∼400-1200 Hz and another branch with frequencies an order of magnitude lower. The frequencies of the high branch ν_h hold a hybrid frequency relation with the Keplerian frequency ν_K: ν²_h=ν²_K+Ω²/π², where Ω is the rotational frequency of the star's magnetosphere. The frequency of the low branch is ν_L=(Ω/π)(ν_K/ν_h)sinδ, where δ is a small angle between Ω 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 ∼35 Hz QPO tracks the frequency of the kilohertz oscillations. We interpret the ∼35 Hz oscillations as ν_L and find δ=3°.9±0°.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 δ is calculated. The inferred angle δ stays approximately the same over the significant range of ν_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 ν_L.