X-ray Eclipses of Active Galactic Nuclei

Abstract

X-ray variation is a ubiquitous feature of active galactic nuclei (AGNs), however, its origin is not well understood. In this paper, we show that the X-ray flux variations in some AGNs, and correspondingly the power spectral densities (PSDs) of the variations, may be interpreted as being caused by absorptions of eclipsing clouds or clumps in the broad line region (BLR) and the dusty torus. By performing Monte-Carlo simulations for a number of plausible cloud models, we systematically investigate the statistics of the X-ray variations resulting from the cloud eclipsing and the PSDs of the variations. For these models, we show that the number of eclipsing events can be significant and the absorption column densities due to those eclipsing clouds can be in the range from 10^{21} to 10^{24} cm^{-2}, leading to significant X-ray variations. We find that the PSDs obtained from the mock observations for the X-ray flux and the absorption column density resulting from these models can be described by a broken double power law, similar to those directly measured from observations of some AGNs. The shape of the PSDs depend strongly on the kinematic structures and the intrinsic properties of the clouds in AGNs. We demonstrate that the X-ray eclipsing model can naturally lead to a strong correlation between the break frequencies (and correspondingly the break timescales) of the PSDs and the masses of the massive black holes (MBHs) in the model AGNs, which can be well consistent with the one obtained from observations. Future studies of the PSDs of the AGN X-ray (and possibly also the optical-UV) flux and column density variations may provide a powerful tool to constrain the structure of the BLR and the torus and to estimate the MBH masses in AGNs.

25 pages, 10 figures

References in corpus (63)

• Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• Active Galactic Nuclei as scaled-up Galactic black holes
• AGN Dusty Tori: I. Handling of Clumpy Media
• The distribution of absorbing column densities among Seyfert 2 galaxies
• Biases in Virial Black Hole Masses: An SDSS Perspective
• The AGN Obscuring Torus -- End of the "Doughnut" Paradigm?
• Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies
• Measuring the broadband power spectra of active galactic nuclei with RXTE
• Black Hole Masses and Eddington Ratios at 0.3<z<4
• Ubiquitous variability of X-ray absorbing column densities in Seyfert 2 Galaxies
• Modeling reverberation mapping data II: dynamical modeling of the Lick AGN Monitoring Project 2008 dataset
• Extreme X-ray spectral variability in the Seyfert 2 Galaxy NGC 1365
• X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
• Occultation measurement of the size of the X-ray emitting region in the Active Galactic Nucleus of NGC 1365
• CAIXA: a catalogue of AGN in the XMM-Newton archive III. Excess Variance Analysis
• First X-ray-Based Statistical Tests for Clumpy-Torus Models: Eclipse Events from 230 Years of Monitoring of Seyfert AGN
• The Sizes of the X-ray and Optical Emission Regions of RXJ1131-1231
• X-ray variability of 104 active galactic nuclei. XMM-Newton power-spectrum density profiles
• Spectral evolution of magnetic flares and time lags in accreting black hole sources
• Correlations between X-ray and radio spectral properties of accreting black holes
• Towards a physical model of dust tori in Active Galactic Nuclei - Radiative transfer calculations for a hydrostatic torus model
• Temporal Properties of Cygnus X-1 During the Spectral Transitions
• The iron line in MCG-6-30-15 from XMM-Newton: evidence for gravitational light-bending?
• An absorption origin for the X-ray spectral variability of MCG-6-30-15
• Variable partial covering and a relativistic iron line in NGC 1365
• "Comets" orbiting a black hole
• X-ray Absorption and Reflection in Active Galactic Nuclei
• Geometric and Dynamical Models of Reverberation Mapping Data
• The Near-Infrared Broad Emission Line Region of Active Galactic Nuclei -- I. The Observations
• The Lick AGN Monitoring Project: Velocity-Delay Maps from the Maximum-Entropy Method for Arp 151
• Rapid N_H changes in NGC 4151
• The relationship between X-ray variability amplitude and black hole mass in active galactic nuclei
• How complex is the obscuration in AGN? New clues from the Suzaku monitoring of the X-ray absorbers in NGC7582
• An Expanded RXTE Survey of X-ray Variability in Seyfert 1 Galaxies
• Long-term variability of AGN at hard X-rays
• The broad band spectral variability of MCG-6-30-15 observed by NuSTAR and XMM-Newton
• On the difference of torus geometry between hidden and non-hidden broad line active galactic nuclei
• A Bayesian Approach to Estimate the Size and Structure of the Broad-line Region in Active Galactic Nuclei Using Reverberation Mapping Data
• The variability plane of accreting compact objects
• Calibrating the correlation between black hole mass and X-ray variability amplitude: X-ray only black hole mass estimates for active galactic nuclei and ultra-luminous X-ray sources
• An absorption event in the X-ray lightcurve of NGC 3227
• Are AGN Broad Emission Lines Formed by Discrete Clouds? --- Analysis of Keck High Resolution Spectroscopy of NGC 4151
• Scaling variability from stellar to supermassive black holes
• The absorption-dominated model for the X-ray spectra of type I active galaxies: MCG-6-30-15
• The properties of the clumpy torus and BLR in the polar-scattered Seyfert 1 galaxy ESO 323-G77 through X-ray absorption variability
• The relationship between the X-ray variability and the central black hole mass
• NLS1 galaxies and estimation of their central black hole masses from the X-ray excess variance method
• The size of the X-ray emitting region in SWIFT J2127.4+5654 via a broad line region cloud X-ray eclipse
• Revealing the X-ray Variability of AGN with Principal Component Analysis
• Characterising the complex absorber in NGC 4151
• X-ray spectral variability of the Seyfert galaxy NGC 4051
• An Occultation Event in Centaurus A and the Clumpy Torus Model
• The effects of X-ray absorption variability in NGC 4395
• Black hole spin and size of the X-ray emitting region(s) in the Seyfert 1.5 galaxy ESO 362-G18
• Is the Broad-Line Region Clumped or Smooth? Constraints from the H alpha Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy
• Short Timescale AGN X-ray Variability with EXOSAT: Black hole mass and Normalised Variability Amplitude
• Quasar Cartography: from Black Hole to Broad Line Region Scales
• X-ray Spectral and Variability Properties of Low-Mass AGN
• Probing general relativistic effects during AGN X-ray eclipses
• The effects of relativistic bulk motion of X-ray flares in the corona on the iron Kalpha line in Seyfert 1 galaxies
• The First Hard X-Ray Power Spectral Density Functions of AGN
• X-ray absorption variability in NGC 4507

Cited by in corpus (5)

• Piercing Through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields: I. X-ray Spectral and Long-term Variability Analyses
• The relativistic jet of the gamma-ray emitting narrow-line Seyfert 1 galaxy 1H 0323+342
• Variation of Broad Emission Lines from QSOs with Optical/UV Periodicity to Test the Interpretation of Supermassive Binary Black Holes
• Update on the X-ray variability plane for active galactic nuclei: The role of the obscuration
• Swift, NuStar and XMM-Newton observations of the NLS1 galaxy RX J2317.8-4422 in an extreme X-ray low flux state