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R. Remillard, E. Morgan, A. Levine, M. Muno (M.I.T.), J. McClintock, G. Sobczak (CFA), J. Orosz (Penn State U.), C. Bailyn (Yale)
We summarize the properties of X-ray QPOs at 67 Hz in GRS1915+105, 300 Hz in GRO J1655-40, and 185 Hz in XTE J1550-564. The QPO detections in GRS1915+105 are by far the most common, with detections on 22 of 234 days with observations by the RXTE PCA instrument between 1996 April and 1999 February. Despite significant changes in X-ray luminosity, the QPO central frequency varies by only a few %. There are occasional degradations of coherence (from Q=30 to Q=6) with little change in central frequency. The fast QPOs in the other two sources are comparatively rare and less coherent (3.2 < Q < 4.0). They only appear with a distinct suite of spectral changes in which the disk appears small and hot while the power law component is strong. We discuss the details of the spectral properties and phase lags of these QPOs with respect to the 'diskoseismic' and 'frame dragging' oscillations predicted by General Relativity.
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