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• W17042970 abstract "Gleissner, Thomas X-ray and Radio Variability of Cygnus X-1 Stellar black holes and neutron stars, so-called compact objects, are the final stages in the evolution of massive stars with more than ∼ 8 solar masses. If the mass of a compact object is greater than the theoretical mass limit of a neutron star, the existence of a black hole is the logical consequence within the framework of the general relativity theory. Cygnus X-1 is an X-ray binary which consists of an O-type supergiant and a black hole accreting mass from its companion. One characteristic of such systems is the powerful emission of temporally and spectrally variable X-ray radiation. Basically, the system can be found in either of two states, referred to as hard state and soft state. Although Cygnus X-1 is to be counted among the best studied black hole X-ray binaries, its exact geometry is not clear, just as for similar sources. A definite constituent of all models is a mass accretion disk releasing soft X-rays. Less agreement exists with regard to where the hard X-rays originate during the hard state. Most models assume regions where soft disk photons are energized by inverse Compton scattering to hard X-rays. In recent years, several X-ray binaries have been detected to possess matter outflows, so-called jets. Apart from open questions concerning their formation, the contribution of jets in the X-ray regime remains to be clarified. The subject of this thesis is the variable emission of Cygnus X-1 in the X-ray and in the radio band. The analyzed data span several years and were taken in an Xray monitoring with the satellite RXTE and simultaneous radio observations with the Ryle Telescope at Cambridge (UK). After an introductory description of the basic issues in chapter 1, the following chapter 2 summarizes the mathematics to describe variability by Fourier analysis as well as theoretical models of variability and of the underlying physical mechanisms. Apart from phenomenological approaches like the shot noise model, a recently discovered linear relationship between the rms variability and the flux of X-ray lightcurves, the so-called rms-flux relation, is outlined. In chapter 3 this relation is investigated using the lightcurves of Cygnus X-1. It is shown that the relationship is valid on all time scales > 5 s, both in the hard state and in the soft state. The existence of a non-zero intercept C on the flux axis argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant variability component. The slope k of the linear rms-flux relation mirrors the fractional variability. The relationship between these two hypothesized components can be described by a fundamental dependence of k and C with" @default.
• W17042970 created "2016-06-24" @default.
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• W17042970 date "2004-01-01" @default.
• W17042970 modified "2023-09-27" @default.
• W17042970 title "X-ray and radio variability of Cygnus X-1" @default.
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