DISCOVERY OF Fe Kα X-RAY REVERBERATION AROUND THE BLACK HOLES IN MCG–5-23-16 AND NGC 7314

Abstract

Several X-ray observations have recently revealed the presence of reverberation time delays between spectral components in active galactic nuclei. 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 Kα line peaks, lags the bands at lower and higher energies with a time delay of ∼1 ks. These lags are unlikely to be due to the narrow Fe Kα line. They are fully consistent with reverberation of the relativistically broadened iron Kα 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.