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Long Term Variability of Cyg X-1, II. The rms-Flux Relation

T. Gleissner·J. Wilms·K. Pottschmidt·P. Uttley·M. A. Nowak·R. Staubert
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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 Uttley & McHardy (2001) 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.

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T. Gleissner, J. Wilms, K. Pottschmidt, P. Uttley, M. A. Nowak, R. Staubert. 2003-11-05. Long Term Variability of Cyg X-1, II. The rms-Flux Relation. https://doi.org/10.1051/0004-6361%3A20031684

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