Discovery of Fe K{\alpha} X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314. (arXiv:1302.1761v1 [astro-ph.HE])

Discovery of Fe K{\alpha} X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314. (arXiv:1302.1761v1 [astro-ph.HE]):
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.