Using a large quantity of Rossi X-ray Timing Explorer data presented in the
literature I offer a detailed investigation into the accuracy of quasiperiodic
oscillations (QPO) frequency determination. The QPO phenomenon seen in X-ray
binaries is possibly a result of the resonance of the intrinsic (eigen)
oscillations and harmonic driving forces of the system. I show that the
resonances, in the presence of the damping of oscillations, occur at the
frequencies which are systematically and randomly shifted with respect to the
eigenfrequencies of the system. The shift value strongly depends on the damping
rate which is measured by the halfwidth of the QPO feature. Taking into account
this effect I analyze the QPO data for four Z-sources: Sco X-1, GX 340+0, GX
5-1, GX 17+2 and two atoll sources: 4U 1728-34, 4U 0614+09. The transition
layer model (TLM) predicts the existence of the invariant quantity: delta, an
inclination angle of the magnetospheric axis with respect to the normal to the
disk. I calculate delta and the error bars of delta using the resonance shift
and I find that the inferred delta-values are consistent with constants for
these four Z-sources, where horizontal branch oscillation and kilohertz
frequencies have been detected and correctly identified. It is shown that the
inferred delta are in the range between 5.5 and 6.5 degrees. I conclude that
the TLM seems to be compatible with data.Comment: 9 pages and 2 figures. Accepted for publication in the Astrophysical
Journal Letters 2002 August 2
