Energy Dependent time lags in the Seyfert 1 galaxy NGC 4593
  We investigate the energy-time lag dependence of the source NGC 4593 using
XMM-{\it Newton}/EPIC-pn data. We found that the time lag dependency is linear
in nature with respect to the logarithm of different energy bands. We also
investigate the frequency dependent time lags and identify that at some
frequency range (5 $\times$ 10$^{-5}$ Hz -- 2 $\times$ 10$^{-4}$ Hz) the X-ray
emission is highly coherent, mildly frequency dependent and very strongly
energy dependent. These observations can be explained in the frame work of the
thermal Comptonization process and they indicate a truncated accretion disk
very close to the black hole. We discuss the plausible spectral state to
explain the phenomenon and conclude that the observed properties bear a close
resemblance to the intermediate state or the steep power-law state, found in
galactic black hole sources.
