X‐Ray Observations of XTE J1550−564 during the Decay of the 2000 Outburst. II. Timing

We investigate the timing behavior of XTE J1550-564 with the Rossi X-rayTiming Explorer (RXTE) as the source made a transition to the hard state duringthe decay of the 2000 outburst. We detect a high frequency QPO at 65 Hz in oneobservation with a fractional rms amplitude of 4.9%. This is the first timethat a high frequency QPO has been detected in a transition to the hard stateduring outburst decay. We also observe low frequency QPOs in the 0.36-4.1 Hzrange and rich aperiodic variability. The changes in the temporal propertiesduring the decay are very similar to the state transitions observed for othersources. We find a correlation between the QPO frequency and the breakfrequency in the continuum power spectra. We investigate the energy dependenceof rms amplitudes of the QPOs. We compare these timing properties with thosepreviously observed for XTE J1550-564 and other Galactic black hole candidatesand discuss the implications for QPO models and black hole accretion.Comment: 7 pages, accepted by ApJ. Minor modifications made after the referee's Comment