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Phase Lag and Coherence Function of X-Ray Emission from Black Hole Candidate XTE J1550-564We report the results from measuring the phase lag and coherence function of X-ray emission from black hole candidate XTE J1550-564. These temporal X-ray properties have been recognized to be increasingly important in providing important diagnostics of the dynamics of accretion flows around black holes. For XTE J1550-564, we found significant hard lag-the X-ray variability in high-energy bands lags behind that in low-energy bands-associated both with broadband variability and quasi-periodic oscillation (QPO) . However, the situation is more complicated for the QPO: while hard lag was measured for the first harmonic of the signal, the fundamental component showed significant soft lag. Such behavior is remarkably similar to what was observed of microquasar GRS 1915+105. The phase lag evolved during the initial rising phase of the 1998 outburst. The magnitude of both the soft and hard lags of the QPO increases with X-ray flux, while the Fourier spectrum of the broadband lag varies significantly in shape. The coherence function is relatively high and roughly constant at low frequencies and begins to drop almost right after the first harmonic of the QPO. It is near unity at the beginning and decreases rapidly during the rising phase. Also observed is that the more widely separated the two energy bands are, the less the coherence function between the two. It is interesting that the coherence function increases significantly at the frequencies of the QPO and its harmonics. We discuss the implications of the results on the models proposed for black hole candidates.
Document ID
20040071154
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cui, Wei
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Zhang, Shuang Nan
Chen, Wan
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 21, 2013
Publication Date
March 1, 2000
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 531
Issue: 1
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAG5-7927
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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