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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint G/01

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

E. Kalemci (1), J.A. Tomsick (1), R.E. Rothschild (1), K. Pottschmidt (2), P. Kaaret (3)

(1) Center for Astrophysics and Space Sciences, Code 0424, University of California at San Diego, La Jolla, CA 92093-0424
(2) Institut für Astronomie und Astrophysik, University of Tübingen, Waldhäuser Straße 64, D-72076 Tübingen, Germany
(3) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138

The Astrophysical Journal 563, 239-245, (2001)

Abstract. We investigate the timing behavior of XTE J1550-564 with the Rossi X-Ray Timing Explorer as the source made a transition to the hard state during the decay of the 2000 outburst. We detect a high-frequency quasi-periodic oscillation (QPO) at 65 Hz in one observation with a fractional rms amplitude of 4.9%. This is the first time that a high-frequency QPO has been detected in a transition to the hard state during outburst decay. We also observe low-frequency QPOs in the 0.36-4.1 Hz range and rich aperiodic variability. The changes in the temporal properties during the decay are very similar to the state transitions observed for other sources. We find a correlation between the low-frequency QPO and the break frequency in the continuum power spectra. We investigate the energy dependence of rms amplitudes of the QPOs. We compare these timing properties with those previously observed for XTE J1550-564 and other Galactic black hole candidates and discuss the implications for QPO models and black hole accretion.

Key words: Black Hole Physics, stars: individual (XTE J1550-564), X-Rays: Stars

Preprint (437 kb gzip'ed Postscript including figures)

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