On the origin of the featureless soft X-ray excess emission from the
  Seyfert 1 galaxy ESO~198--G24
  We present medium and high resolution X-ray spectral study of a Seyfert 1
galaxy ESO~198--G24 using a long (122 ks) XMM-Newton observation performed in
February 2006. The source has a prominent featureless soft X-ray excess below
$2\kev$. This makes the source well suited to investigate the origin of the
soft excess. Two physical models -- blurred reflection, and optically thick
thermal Comptonization in a warm plasma, describe the soft-excess equally well
resulting in similar fits in the $0.3-10\kev$ band. These models also yield
similar fits to the broad-band UV (Optical Monitor) and X-ray data. XMM-Newton
observations performed in 2000, 2001 and 2006 on this source show flux
variability. From 2001 to 2006, the UV flux increased by $\sim23\%$ while the
$2-10\kev$ X-ray flux as well as the soft-excess flux decreased by ~ 20. This
observation can be described in the blurred reflection scenario by a truncated
accretion disk whose inner-most radius had come closer to the blackhole. We
find that the best-fit inner radius of the accretion disk decreases from
R_{in}=4.93_{-1.10}^{+1.12}R_G to R_{in}<2.5R_G from 2001 to 2006. This leads
to an increase in the UV flux and compressing the corona, leading to reduction
of the powerlaw flux and therefore the soft-excess. The blurred reflection
model seems to better describe the soft-excess for this source.
