2004A&A...426..587C

We present the results of an extensive timing analysis of the 1999 outburst of the soft X-ray transient and black hole candidate XTE J1859+226 as observed with the Rossi X-Ray Timing Explorer. Three main different types of low frequency (1-9Hz) quasi-periodic oscillations (QPOs) were observed and classified, strengthening the general picture that is emerging for the variability properties of black hole X-ray binaires. Rapid transitions between different power spectral shapes were observed and their link with the count rate was studied. Furthermore, we show that a frequency of ∼6Hz seems to hold a particular place: one of the three QPO types we found was very stable when at this frequency, as it happens in Z sources as well. The coherence of its subharmonic peak was higher when the fundamental was close to 6Hz, thus suggesting the presence of some resonance at this frequency.