  We observed the low mass X-ray binary Cyg X-2 for a total of 18 nights over
two observing runs in July and September of 2006, using the Otto Struve
Telescope at McDonald Observatory and the Rossi X-ray Timing Explorer. Using
discrete cross correlations, we found peaks occurring at near-zero lags in the
flaring branch of the colour-colour diagram, which could signify reprocessing,
in addition to an anti-correlation within the normal branch. When comparing
optical flux to the system's placement on the Z track, two distinct behaviors
were seen: (1) a state with no correlation, and (2) a multi-valued (horizontal
and normal branches)/correlated (flaring branch) state. The correlation was the
result of direct steps and more gradual falls to and from the flaring branch
respectively. Finally, we modeled timed spectra with 64 second bins with an
extended accretion disc corona model. We found that correlations occurred
between the optical and the various fitted parameters, particularly the
blackbody normalization (and blackbody radius by extension) in higher intensity
regions. Despite this, the Z track location was found to be a far better
predictor of physical parameters than the optical flux, with clean correlations
seen in every branch of the Z track. Where optical correlations are found, the
location on the Z track was a better predictor of optical flux than any
individual physical parameter.
