Long term variability of Cyg X-1. II. The rms-flux relation
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Gleissner, T., J. Wilms, K. Pottschmidt, P. Uttley, M. A. Nowak, and R. Staubert. “Long Term Variability of Cyg X-1 - II. The Rms-Flux Relation.” Astronomy & Astrophysics 414, no. 3 (February 1, 2004): 1091–1104. https://doi.org/10.1051/0004-6361:20031684.
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Attribution 4.0 International (CC BY 4.0)
Attribution 4.0 International (CC BY 4.0)
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Abstract
We study the long term evolution of the relationship between the root mean square (rms) variability and flux (the “rms-flux relation”) for the black hole Cygnus X-1 as monitored from 1996 to 2003 with the Rossi X-ray Timing Explorer (RXTE). We confirm earlier results by [CITE] of a linear relationship between rms and flux in the hard state on time scales >5 s reflecting in its slope the fractional rms variability. We demonstrate the perpetuation of the linear rms-flux relation in the soft and the intermediate state. The existence of a non-zero intercept in the linear rms-flux relation argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant rms component. The relationship between these two hypothesized components can be described by a fundamental dependence of slope and intercept at time scales <∼10 ksec with long term averages of the flux.