  The neutron star X-ray binary (NSXRB) Cygnus X-2 was observed by the Swift
satellite 51 times over a 4 month period in 2008 with the XRT, UVOT, and BAT
instruments. During this campaign, we observed Cyg X-2 in all three branches of
the Z track (horizontal, normal, and flaring branches). We find that the NUV
emission is uncorrelated with the soft X-ray flux detected with the XRT, and is
anticorrelated with the BAT X-ray flux and the hard X-ray color. The observed
anticorrelation is inconsistent with simple models of reprocessing as the
source of the NUV emission. The anticorrelation may be a consequence of the
high inclination angle of Cyg X-2, where NUV emission is preferentially
scattered by a corona that expands as the disk is radiatively heated.
Alternatively, if the accretion disk thickens as Cyg X-2 goes down the normal
branch toward the flaring branch, this may be able to explain the observed
anticorrelation. In these models the NUV emission may not be a good proxy for
$\dot m$ in the system. We also discuss the implications of using Swift/XRT to
perform spectral modeling of the continuum emission of NSXRBs.
