X-ray timing and spectral analysis of reverberating active galactic nuclei

Abstract

ABSTRACT We use the publicly available XMM–Newton archive to select a sample of 20 active galactic nuclei (AGNs) known to exhibit reverberation signatures caused by the reflection of X-rays from the corona off the accretion disc that feeds the central black hole engine. Inverse Compton scattering by energetic electrons, coupled with accretion disc fluctuations give rise to the highly variable observed X-ray spectrum, the behaviour of which is still not fully understood. We use 121 observations in 3–4 distinct spectral states for each source and calculate the time lags as a function of frequency. We fit the relativistic reflection model RELXILL and explore parameter correlations. The known scaling relationship between the black hole mass and time lag is well recovered and the continuum flux is coupled strongly to the disc reflection flux. We also find that 1H 0707−495 and IRAS 13224−3809 are well described using reflection and absorption modelling in a variety of flux states. The reflection fraction is strongly coupled to the power-law photon index and may be linked to dynamics of the emitting region. The data reveal hints of the power law evolutionary turnover when the 2–10 keV Eddington fraction is ∼0.02, the origin of which is not fully understood. Finally, we report the covering fraction is inversely correlated with the flux and power-law photon index in IRAS 13224−3809. These findings support recent studies of 1H 0707−495 where the covering fraction may contribute to the observed variability via flux modulations from non-uniform orbiting clouds.