The Long-Term Light Curves of X-Ray Binaries Contain Simultaneous Periodic and Random Components

• Published in: The Astrophysical journal Vol. 612; no. 2; pp. 1006 - 1017
• Main Authors: Boyd, Patricia T, Smale, Alan P
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 10.09.2004; University of Chicago Press
• Subjects: Astronomy; Binary and multiple stars; Earth, ocean, space; Exact sciences and technology; Stars; X-ray binaries; X-ray binary stars; Light curves; Binary X ray source; Cosmic x-ray sources; Close binary stars; Long term variation; Accretion disks; Phase space; X ray emission
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/421078

LMC X-3 and Cyg X-2 show large-amplitude X-ray fluctuations that have been attributed to a warped accretion disk. Cyg X-3 displays high-amplitude, apparently nonperiodic oscillations. We reanalyze these systems using RXTE ASM data and time-frequency decomposition techniques. We find that the long- term variations in Cyg X-2 can be completely characterized by excursions whose durations are integer multiples of the orbital period, including one essentially identical to the reported "period" of 78 days. Cyg X-3 can be characterized in terms of integer multiples of a 71 day fundamental period, unrelated to the 4.8 day orbital period, but suggestively close to the > ~60 day reported precession period of the relativistic jet inferred from recent radio observations. The long-term excursions of LMC X-3 are related to each other by rational fractions, suggesting the characteristic timescale is 10.6 days, shorter than any observed excursion to date. We explore the phase-space evolution of the light curves, using a natural embedding, and find that all three systems possess two rotation centers that organize the phase-space trajectories, one of low luminosity and the other of high luminosity. The implications of this repeatable behavior on generic models of accretion disk dynamics and mass transfer variability are explored.