Characterizing the Low-Frequency QPO behavior of the X-ray Nova XTE   J1550-564
  For all 209 RXTE observations of the 7-Crab X-ray nova XTE J1550-564, we analyzed the X-ray power spectra, phase lags, and coherence functions. These observations cover the entire 250 day outburst cycle of the source and are the most complete and arguably the richest data set for any black hole X-ray nova. We find that there are three fundamental types of QPO behavior--one more than reported by Wijnands, Homan, & van der Klis (1999, ApJ, 526, 33). The new type occurred during the first half of the outburst. These three types of QPO behavior can be grouped according to the relative contributions of the disk and power-law components to the total flux. 
Gregory J. Sobczak (Harvard), Ronald A. Remillard (MIT), Michael P.   Muno (MIT), Jeffrey E. McClintock (CfA)