RXTE Observations of LMC X-1
  The luminous X-ray binary and black-hole candidate LMC X-1 has been observed with the Rossi X-ray Timing Explorer (RXTE) to search for quasi-periodic oscillations (QPO), previously reported in its high state. The source was observed monthly in a series of nine observations. Analysis of the temporal variations shows no evidence for QPO or other periodic changes, but correlations between the high-energy light curve and hardness of the spectrum are described. Spectral fits with two-component models demonstrate that the hardness variations come from changes in the intensity of the high-energy power-law tail. 
P. C. Schmidtke, A. L. Ponder, A. P. Cowley