Correlation between Break Frequency and Power Density Spectrum Slope for the X-ray Source Cygnus X-2: RXTE/PCA Data

We present results of RXTE observations of the X-ray source Cyg X-2 during 1996–1999. Its power density spectra in the 0.1–128-Hz band are fitted by a model that takes into account the power-law spectral behavior at frequencies below and above the break frequency, with an introduction of one or more Lorenz lines to describe the peaks of quasi-periodic oscillations that correspond to the horizontal branch of the Z track. The RXTE observations have revealed a positive correlation between the break frequency and the indices of the two parts of the spectrum. The spectrum steepens with increasing break frequency both above and below the break frequency.