期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 697, 期 2, 页码 L167-L172出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/697/2/L167
关键词
accretion, accretion disks; black hole physics; stars: individual (XTE J1118+480, GX339-4, Swift J1753.5-0127); X-rays: binaries
资金
- STFC [PP/D002370/1]
- STFC [PP/D002370/1] Funding Source: UKRI
- Science and Technology Facilities Council [PP/D002370/1] Funding Source: researchfish
A linear relation between absolute rms variability and flux in X-ray observations of compact accreting sources has recently been identified. Such a relation suggests that X-ray light curves are nonlinear and composed of a lognormal distribution of fluxes. Here, a first investigation of the optical rms versus flux behavior in X-ray binaries is presented. Fast timing data on three binaries in the X-ray low/hard state are examined. These are XTE J1118+ 480, GX 339-4, and SWIFT J1753.5-0129-all show aperiodic (nonreprocessed) optical fluctuation components. Optical rms amplitude is found to increase with flux in all sources. A linear fit results in a positive offset along the flux axis, for most frequency ranges investigated. The X-ray and optical relation slopes track the source fractional variability amplitudes. This is especially clear in the case of GX 339-4, which has the largest optical variance of the three targets. Nonlinearity is supported in all cases by the fact that flux distributions of the optical light curves are better described with a lognormal function than a simple Gaussian. Significant scatter around linearity is found in the relation for the two sources with lower optical variability amplitude, though observational biases may well contribute to this. Implications for accretion models are discussed, and the need for long well sampled optical light curves is emphasized.
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