Open AccessLong‐term properties of accretion discs in X‐ray binaries – I. The variable third period in SMC X‐1
Author(s) -
Clarkson W. I.,
Charles P. A.,
Coe M. J.,
Laycock S.,
Tout M. D.,
Wilson C. A.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06176.x
Subject(s) - physics , astrophysics , context (archaeology) , observatory , accretion (finance) , astronomy , accretion disc , sky , paleontology , biology
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.