  The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were
monitored for 35 days and 12 days with ASCA and RXTE (and EUVE for Ton S180).
The short time scale (hours-days) variability patterns were very similar across
energy bands, with no evidence of lags between any of the energy bands studied.
The fractional variability amplitude was almost independent of energy band. It
is difficult to simultaneously explain soft Seyferts stronger variability,
softer spectra, and weaker energy-dependence of the variability relative to
hard Seyferts. The soft and hard band light curves diverged on the longest time
scales probed, consistent with the fluctuation power density spectra that
showed relatively greater power on long time scales in the softest bands. The
simplest explanation is that a relatively hard, rapidly-variable component
dominates the total X-ray spectrum and a slowly-variable soft excess is present
in the lowest energy channels of ASCA. Although it would be natural to identify
the latter with an accretion disk and the former with a corona surrounding it,
a standard thin disk could not get hot enough to radiate significantly in the
ASCA band, and the observed variability time scales are much too short. The
hard component may have a more complex shape than a pure power-law. The most
rapid factor of 2 flares and dips occurred within ~1000 sec in Ark 564 and a
bit more slowly in Ton S180. The speed of the luminosity changes rules out
viscous or thermal processes and limits the size of the individual emission
regions to <~15 Schwarzschild radii (and probably much less), that is, to
either the inner disk or small regions in a corona.
