Detecting X-ray QPOs in Active Galaxies
  Since EXOSAT produced the first good quality X-ray light curves of Seyfert galaxies there have been several claims of quasi-periodic oscillations (QPOs). None of these have withstood repeated analyses and observations. We review some problems concerning the detection of QPOs. 
S. Vaughan (1), P. Uttley (2) ((1) University of Leicester, (2)   NASA-GSFC)