The power spectral properties of the Z source GX 340+0

We present an analysis of similar to 390 ks of data of the Z source GX 3400 taken during 24 observations with the Rossi X-Ray Timing Explorer satelli te. We report the discovery of a new broad component in the power spectra. The frequency of this component varied between 9 and 14 Hz and remained clo se to half that of the horizontal-branch quasi-periodic oscillations (HBOs) . Its rms amplitude was consistent with being constant around similar to 5% , while its FWHM increased with frequency from 7 to 18 Hz. If this sub-HBO component is the fundamental frequency, then the HBO and its second harmoni c are the second and fourth harmonic component, while the third harmonic wa s not detected. This is similar to what was recently found for the black ho le candidate XTE J1550-564. The profiles of both the horizontal- and the no rmal-branch quasi-periodic oscillation peaks were asymmetric when they were strongest. We describe this in terms of a shoulder component at the high-f requency side of the quasiperiodic oscillation peak, of which the rms ampli tudes were approximately constant at similar to 4% and similar to 3%, respe ctively. The peak separation between the twin kilohertz quasi-periodic osci llations was consistent with being constant at 339+/-8 Hz, but a trend simi lar to that seen in, e.g., Sco X-l could not be excluded. We discuss our re sults within the framework of the various models that have been proposed fo r the kilohertz QPOs and low-frequency peaks.