Evolution of the 0.01 - 25 Hz power spectral components in Cygnus X-1
  Analyzing the archival data from the Rossi X-ray Timing Explorer (RXTE), we study the power density spectra (PDS) of Cygnus X-1 from 1996 to 2003 in the frequency range of 0.01 - 25 Hz. With our model we are able to track the evolution of the Lorentzian components through all spectral states of the source. We confirm the relation between characteristic frequencies seen both in black hole candidate and neutron star sources, and show the changes in this relation during the transitional and soft states of the source. The connection between the Lorentzian components is investigated by analyzing similarities and differences in their behavior. We find that the spectral state of the source can be uniquely determined from the parameters of the these components. The parameter correlations can all be described by continuous functions, which differ between components. We discuss our results in the context of relativistic precession model for the accretion disk, and show a remarkable agreement between the model prediction and the data in the hard state. We estimate a value for the specific angular momentum of a=+0.49 (-0.57) in the case of prograde retrograde) rotation and an estimate for the inner radius of 22 to 50 (25 to 55) gravitational radii. 
M. Axelsson, L. Borgonovo and S. Larsson (Stockholm Observatory)