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The ABC of low-frequency quasi-periodic oscillations in Black-Hole Candidates: analogies with Z-sources

P. Casella·T. Belloni·L. Stella
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Abstract

Three main types of low-frequency quasi-periodic oscillations (LFQPOs) have been observed in Black Hole Candidates. We re-analyzed RXTE data of the bright systems XTE J1859+226, XTE J1550-564 and GX 339-4, which show all three of them. We review the main properties of these LFQPOs and show that they follow a well-defined correlation in a fractional rms vs. softness diagram. We show that the frequency behavior through this correlation presents clear analogies with that of Horizontal-, Normal- and Flaring-Branch Oscillations in Z sources, with the inverse of the fractional rms being the equivalent of the curvilinear coordinate Sz through the Z track.

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P. Casella, T. Belloni, L. Stella. 2005-04-14. The ABC of low-frequency quasi-periodic oscillations in Black-Hole Candidates: analogies with Z-sources. https://doi.org/10.1086/431174

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