In this paper, results from temporal analysis of RXTE observations of the black hole binary Cygnus X‐l are reviewed. By tapping into the large amount of archival data available, a systematic study of the variability, in the form of the power spectrum, is conducted. It is clear that timing studies can give valuable information on the emission mechanisms and accretion geometry. Tying characteristic frequencies to effects predicted by general relativity directly gives information about the parameters of the compact object.
The results show that the characteristic frequencies seen in the power spectrum follow the relation predicted for the nodal and periastron precessional frequencies of relativistic precession. From this relation, the spin of the black hole is determined to for a mass of 9 M⊙. During times of high hardness, the hardness‐flux correlation seen in the hard state of the source disappears on short timescales. Together with the variable characteristic frequencies, this is interpreted as support for the truncated disk scenario.
