We have studied the time evolution of the power spectrum of XTE J1550-564,
using X-ray luminosity time series data obtained by the Rossi X-Ray Timing
Explorer satellite. A number of important practical fundamental issues arise in
the analysis of these data, including dealing with time-tagged event data,
removal of noise from a highly non-stationary signal, and comparison of
different time-frequency distributions. We present two new methods to
understand the time frequency variations, and compare them to the dynamic power
spectrum of Homan et al. All of the approaches provide evidence that the QPO
frequency varies in a systematic way during the time evolution of the signal.Comment: 4 pages, 3 figures; 2001 IEEE - EURASIP Workshop on Nonlinear Signal
and Image Processing (June 3-6, 2001), and to appear in the proceeding
