We study the soft X-ray variability of Cygnus X-3 .
By combining data from the All-Sky Monitor and Proportional Counter Array instruments on the RXTE satellite with EXOSAT Medium Energy ( ME ) detector observations , we are able to analyse the power density spectrum ( PDS ) of the source from 10 ^ { -9 } -0.1 Hz , thus covering time-scales from seconds to years .
As the data on the longer time-scales are unevenly sampled , we combine traditional power spectral techniques with simulations to analyse the variability in this range .
The PDS at higher frequencies ( \ga 10 ^ { -3 } Hz ) are for the first time compared for all states of this source .
We find that it is for all states well-described by a power-law , with index \sim - 2 in the soft states and a tendency for a less steep power-law in the hard state .
At longer time-scales , we study the effect of the state transitions on the PDS , and find that the variability below \sim 10 ^ { -7 } Hz is dominated by the transitions .
Furthermore , we find no correlation between the length of a high/soft state episode and the time since the previous high/soft state .
On intermediate time-scales we find evidence for a break in the PDS at time-scales of the order of the orbital period .
This may be interpreted as evidence for the existence of a tidal resonance in the accretion disc around the compact object , and constraining the mass ratio to M _ { 2 } / M _ { 1 } \la 0.3 .