  We report the results of intensive X-ray, UV and optical monitoring of the
Seyfert 1 galaxy NGC 4593 with Swift. There is no intrinsic flux-related
spectral change in the the variable components in any band with small apparent
variations due only to contamination by a second constant component, possibly a
(hard) reflection component in the X-rays and the (red) host galaxy in the
UV/optical bands. Relative to the shortest wavelength band, UVW2, the lags of
the other UV and optical bands are mostly in agreement with the predictions of
reprocessing of high energy emission from an accretion disc. The U-band lag is,
however, far larger than expected, almost certainly because of reprocessed
Balmer continuum emission from the more distant broad line region gas. The UVW2
band is well correlated with the X-rays but lags by ~6x more than expected if
the UVW2 results from reprocessing of X-rays on the accretion disc. However, if
the lightcurves are filtered to remove variations on timescales >5d, the lag
approaches the expectation from disc reprocessing. MEMEcho analysis shows that
direct X-rays can be the driver of most of the variations in the UV/optical
bands as long as the response functions for those bands all have long tails (up
to 10d) in addition to a strong peak (from disc reprocessing) at short lag
(<1d). We interpret the tails as due to reprocessing from the surrounding gas.
Comparison of X-ray to UVW2 and UVW2 to V-band lags for 4 AGN, including NGC
4593, shows that all have UVW2 to V-band lags which exceed the expectations
from disc resprocessing by factor < 2. However the X-ray to UVW2 lags are,
mostly, in greater excess from the expectations from disc reprocessing and
differ between AGN. The largest excess is in NGC 4151. Absorption and
scattering may be affecting X-ray to UV lags.
