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

Abstract

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 Δt ∼ 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.

A comprehensive approach to analyzing theXMM-Newtondata of Seyfert 1 galaxies

“…They found similar parameters for the Fe line profile: a narrow line (with the line width unresolved within the energy resolution of the EPIC-pn detector), a central energy of 6.4 +0.02 −0.04 keV, and an EW of 52 +18 −16 eV. Our line parameters are also in good agreement with those more recently given by de Marco et al (2009): E Fe = 6.41 ± 0.04 keV, σ < 0.13 keV, and EW = 46 ± 131.4 eV.…”

A Stochastic Model for the Luminosity Fluctuations of Accreting Black Holes

“…The XMM-Newton 2-10 keV background-subtracted light curves were extracted using the standard routines of the XMM Scientific Analysis System and were binned every 48 s. Both the RXTE and XMM-Newton light curves were fit simultaneously. The XMM-Newton 2-10 keV count rates were converted to 2-10 keV fluxes using the 2-10 keV flux values calculated by de Marco et al (2009), with the exception of NGC 5506, where we used the value calculated by Guainazzi et al (2010). calculated the 2-10 keV luminosities based on the best-fit spectral model to the 3-20 keV PCA data.…”

FERO: Finding extreme relativistic objects

“…A recent paper by De Marco et al (2009) carried out a systematic search for the presence of red-or blue-shifted components in the timeaveraged spectra of the sources in the flux-limited sample. The study also looks into the spectral variability of these spectral components.…”