Energy Dependent time lags in the Seyfert 1 galaxy NGC 4593

Abstract

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.