Search for X-ray occultations in Active Galactic Nuclei

Abstract

Recent time-resolved spectral studies of a few Active Galactic Nuclei in hard X-rays revealed occultations of the X-ray primary source probably by Broad Line Region (BLR) clouds. An important open question on the structure of the circumnuclear medium of AGN is whether this phenomenon is common, i.e. whether a significant fraction of the X-ray absorption in AGN is due to BLR clouds. Here we present the first attempt to perform this kind of analysis in a homogeneous way, on a statistically representative sample of AGN, consisting of the ~40 brightest sources with long XMM-Newton and/or Suzaku observations. We describe our method, based on a simple analysis of hardness-ratio light curves, and its validation through a complete spectroscopic analysis of a few cases. We find that X-ray eclipses, most probably due to clouds at the distance of the BLR, are common in sources where the expected occultation time is compatible with the observation time, while they are not found in sources with longer estimated occultation times. Overall, our results show that occultations by BLR clouds may be responsible for most of the observed X-ray spectral variability at energies higher than 2 keV, on time scales longer than a few ks.

Accepted for publication in MNRAS. 15 pages, 7 figures. Table 2 not included, will be available in the published version. Please contact the authors if you need it in advance of publication

References in corpus (8)

• Occultation measurement of the size of the X-ray emitting region in the Active Galactic Nucleus of NGC 1365
• A Reverberation-Based Mass for the Central Black Hole in NGC 4151
• XMM-Newton study of the complex and variable spectrum of NGC 4051
• The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from Reverberation Mapping
• Rapid N_H changes in NGC 4151
• The Black Hole Mass of NGC 4151: Comparison of Reverberation Mapping and Stellar Dynamical Measurements
• First high energy observations of Narrow Line Seyfert 1s with INTEGRAL/IBIS
• XMM-Newton broad-band observations of NGC 7582: Nh variations and fading out of the active nucleus

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• An X-ray variable absorber within the Broad Line Region in Fairall 51
• On the dynamics of clouds in the broad-line region of AGNs with an ADAF atmosphere
• The XMM deep survey in the CDF-S. X. X-ray variability of bright sources
• Multi-epoch hard X-ray view of Compton-thick AGN Circinus Galaxy
• Mining the XRT archive to probe the X-ray absorber structure in the AGN population