Discovery of Fe K-alpha X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314

TL;DR

This paper reports the discovery of Fe K-alpha X-ray reverberation lags in two active galactic nuclei, providing insights into the proximity of X-ray emission regions to the black holes.

Contribution

It presents the first detection of Fe K reverberation lags in MCG-5-23-16 and NGC 7314, advancing understanding of the inner accretion disk structure.

Findings

Reverberation lags of ~1 kilo-second detected in Fe K band.

Lags are consistent with relativistically-broadened iron K line reverberation.

Emission regions are located at approximately 5 and 24 gravitational radii.

Abstract

Several X-ray observations have recently revealed the presence of reverberation time delays between spectral components in AGN. Most of the observed lags are between the power-law Comptonization component, seen directly, and the soft excess produced by reflection in the vicinity of the black hole. NGC 4151 was the first object to show these lags in the iron K band. Here, we report the discovery of reverberation lags in the Fe K band in two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band, where the Fe K line peaks, lags the bands at lower and higher energies with a time delay of ~ 1 kilo-seconds. These lags are unlikely to be due to the narrow Fe K line. They are fully consistent with reverberation of the relativistically-broadened iron K line. The measured lags, their time-scale and spectral modeling, indicate that most of the radiation is emitted at ~ 5 and 24 gravitational radii for MCG-5-23-16 and NGC 7314 respectively.