High‐Frequency Quasi‐Periodic Oscillations in the 2000 Outburst of the Galactic Microquasar XTE J1550−564

We present an analysis of the high frequency timing properties of theApril-May 2000 outburst of the black hole candidate and Galactic microquasarXTE J1550-564, measured with the Rossi X-ray Timing Explorer. The rapid X-rayvariability we measure is consistent with the source being in either the ``veryhigh'' or ``intermediate'' black hole state. Strong (5-8% rms) quasi-periodicoscillations (QPOs) are found between 249-276 Hz; this represents the firstdetection of the same high frequency QPO in subsequent outbursts of a transientblack hole candidate. We also present evidence for lower-frequency QPOs atapproximately 188 Hz (3.5 sigma, single trial), also reported previously andlikely present simultaneously with the higher-frequency QPOs. We discuss thesefindings within the context of the 1998 outburst of XTE J1550-564, and commenton implications for models of QPOs, accretion flows, and black hole spin.Comment: 14 pages, 4 figures; minor changes from initial version; accepted for publication in the Astrophysical Journa