Long-term properties of accretion discs in X-ray binaries - I.The variable third period in SMC X-1

Clarkson, W.I., Charles, P., Coe, M.J., Laycock, S., Tout, M.D. and Wilson, C.A. (2003) Long-term properties of accretion discs in X-ray binaries - I.The variable third period in SMC X-1. Monthly Notices of the Royal Astronomical Society, 339 (2), 447-454. (doi:10.1046/j.1365-8711.2003.06176.x).

Abstract

Long-term X-ray monitoring data from the Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor (ASM) and the Compton Gamma Ray Observatory (CGRO) Burst And Transient Source Experiment (BATSE) reveal that the third (superorbital) period in SMC X-1 is not constant, but varies between 40 and 60 d. A dynamic power spectrum analysis indicates that the third period has been present continuously throughout the five years of ASM observations. This period changed smoothly from 60 to 45 d and then returned to its former value, on a time-scale of approximately 1600 d. During the nearly 4 yr of overlap between the CGRO and RXTE missions, the simultaneous BATSE hard X-ray data confirm and extend this variation in SMC X-1. Our discovery of such an instability in the superorbital period of SMC X-1 is
interpreted in the context of recent theoretical studies of warped, precessing accretion discs. We find that the behaviour of SMC X-1 is consistent with a radiation-driven warping model.

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Contributors

Author: M.J. Coe

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