CORRELATED X-RAY SPECTRAL AND FAST-TIMING BEHAVIOR OF 4U-1636-53

We present a study of the persistent X-ray emission from the low-mass X-ray binary 4U 1636-53 based on the entire archival EXOSAT ME data se t. We performed a homogeneous analysis of all five EXOSAT observations in terms of the correlated rapid X-ray variability and X-ray spectral properties by means of power spectra, and colour-colour and hardness- intensity diagrams, respectively Over the years we find similar patter ns in the colour-colour diagram and the hardness-intensity diagram, bu t small shifts in their positions occur. We find one case of an island -banana transition. On all but one occasion the differences in colours are smaller than 5%. Between the two ''island state'' data sets we fi nd a shift of 8% in the soft colour, which must be at least partly int rinsic. Clear correlations are present between the X-ray colours (whic h are governed by the mass accretion rate) and the power spectrum. Wit h increasing mass accretion rate the fractional rms amplitude of the p ower-law shaped power spectral component that dominates the power spec tra below similar to 1 Hz rises, while the band-limited noise componen t at higher frequencies drops. The cut-off frequency of the band-limit ed component increases when its amplitude decreases. This is reminisce nt of the behaviour of black-hole candidates in the low state.