INTEGRAL and RXTE power spectra of Cygnus X-1

We evaluate 0.03–20 Hz power spectra of the bright black hole binary Cyg X-1 obtained from non-deconvolved INTEGRAL-ISGRI event data. The ISGRI power spectra are compared to contemporary RXTE-PCA ones in the same hard X-ray energy band of 15–70 keV. They agree well in shape. Since the ISGRI power spectrum of Cyg X-1 is not background corrected it lies about an order of magnitude below the PCA values. In 2003 a soft outburst of Cyg X-1 occurred. From the RXTE-ASM and Ryle radio long term lightcurves and the RXTE spectra we see a canonical “hard state–intermediate state–soft state” evolution. We discuss the evolution of the power spectra in the 15–70 keV range which so far is much less well studied than that at softer energies. We interpret our results regarding the origin of certain variability components.