Characterising anomalous transport in accretion disks from X-ray observations

We examine the time variation of the total X-ray flux from three sources and find that the signal from the Crab (non-accreting) is uncorrelated, the Cygnus X-1 signal is correlated on timescales up to three years, and in the GRS1915+105 signal correlation may extend to only a few days. The method we use also quantifies the distributions of fluctuations and hence constrains turbulence/instability models of accretion disks.