Energy Dependent time lags in the Seyfert 1 galaxy NGC 4593

TL;DR

This study analyzes energy-dependent time lags in the Seyfert 1 galaxy NGC 4593, revealing linear lag behavior with energy, frequency-dependent coherence, and implications for accretion disk structure near the black hole.

Contribution

It demonstrates the energy and frequency dependence of X-ray time lags in NGC 4593, supporting a truncated accretion disk model close to the black hole.

Findings

Time lag dependence is linear with respect to the logarithm of energy.

High coherence observed at specific frequency ranges.

Results suggest a truncated accretion disk near the black hole.

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.