Reflection and noise in Cygnus X-1

We analyzed RXTE/PCA observations of Cyg X-1 from 1996-1998. We found a tig ht correlation between the characteristic noise frequencies (e.g. the break frequency nu(br)) and the spectral parameters in the low spectral state. T he amplitude of reflection increases and the spectrum of primary radiation steepens as the noise frequency increases (nu(br) changes by a factor of si milar to 15 in our sample). This can be understood assuming that increase o f the noise frequency is associated with the shift of the inner boundary of the optically thick accretion disk towards the compact object. The related increase of the solid angle, subtended by the disk, and of the influx of t he soft photons to the Comptonization region lead to an increase of the amo unt of reflection and steepening of the Comptonized spectrum. The correlati on between the slope of primary radiation and the amplitude of reflection e xtends to the soft spectral state. A similar correlation between reflection and slope was found for the freque ncy resolved spectra in the 0.01-15 Hz frequency range. Such a correlation could appear if the longer time scale variations are associated with emissi on originating closer to the optically thick disk and, therefore, having st eeper Comptonized spectra with larger reflection.