Probing variability patterns of the Fe K line complex in bright nearby AGNs

Context: The unprecedented sensitivity of current X-ray telescopes allows the issue of the Fe K line complex variability patterns in bright, nearby AGNs to be addressed for the first time. These kinds of studies have the potential to map the accretion flow in the strong gravity regime of supermassive black holes.
Aims: We examine XMM-Newton observations of the brightest sources of the FERO sample of radio-quiet type 1 AGNs (for a total of 72 observations) with the aim of characterizing the temporal behaviour of Fe K complex features.
Methods: A systematic mapping of residual flux above and below the continuum in the 4-9 keV range was performed in the time vs. energy domain, with the purpose of identifying interesting spectral features in the three energy bands: 5.4-6.1 keV, 6.1-6.8 keV, and 6.8-7.2 keV, respectively corresponding to the redshifted, rest-frame, and either blueshifted or highly ionized Fe Kα line bands. The variability significance of rest frame and energy-shifted Fe K lines was assessed by extracting light curves and comparing them with Monte Carlo simulations.
Results: The time-averaged profile of the Fe K complex revealed spectral complexity in several observations. Red- and blue- shifted components (either in emission or absorption) were observed in 30 out of 72 observations, with an average < EW> ~ 90 eV for emission and < EW> ~ -30 eV for absorption features. We detected significant line variability (with confidence levels ranging between 90% and 99.7%) within at least one of the above energy bands in 26 out of 72 observations on time scales of Δ t ~ 6-30 ks. The reliability of these features has been carefully calculated using this sample and assessed at ~3σ confidence level.
Conclusions: This work increases the currently scanty number of detections of variable, energy-shifted Fe lines and confirms the reliability of the claimed detections. We found that the distribution of detected features is peaked at high variability significances in the red- and blue- shifted energy bands rather than at rest-frame energies, suggesting an origin in a relativistically modified accretion flow.

Figures 5-9, Tables 2, 3 and Appendix A are only available in electronic form at http://www.aanda.org