Variable Iron K-alpha Lines in Seyfert 1 Galaxies

Abstract

We find that variability of the iron K-alpha line is common in Seyfert 1 galaxies. Using data from the ASCA archive for objects that have been observed more than once during the mission, we study the time-averaged spectra from individual observations, thereby probing variability on timescales that range from days to years. Since the statistics of the data do not warrant searches for line variability in terms of a complex physical model, we use a a simple Gaussian to model the gross shape of the line, and then use the centroid energy, intensity and equivalent width as robust indicators of changes in the line profile. We find that ~70% of Seyfert 1s (ten out of fifteen) show variability in at least one of these parameters: the centroid energy, intensity, and equivalent width vary in six, four, and eight sources respectively. Due to the low S/N, limited sampling and time averaging, we consider these results to represent lower limits to the rate of incidence of variability. In most cases changes in the line do not appear to track changes in the continuum. In particular, we find no evidence for variability of the line intensity in NGC 4151, suggesting an origin in a region larger than the putative accretion disk, where most of the iron line has been thought to originate. Mkn 279 is investigated on short timescales. The time-averaged effective line energy is 6.5 keV in the galaxy rest frame. As the continuum flux increases by 20% in a few hours, the Fe K line responds with the effective line energy increasing by 0.22 keV (~10,500 km s^-1). Problems with the ASCA and Rosat calibration that affect simultaneous spectral fits are discussed in an appendix.

26 pages, 30 figures, accepted for publication in the Astrophysical Journal

References in corpus (2)

• The Origin of the X-ray and Ultraviolet Emission in NGC 7469
• Accretion disk models and their X-ray reflection signatures. I. Local spectra

Cited by in corpus (61)

• A fundamental plane of black hole activity
• An X-ray Spectral Model for Compton-Thick Toroidal Reprocessors
• Chandra Snapshot Observations of Low-Luminosity AGNs with a Compact Radio Source
• Imaging Optically-Thin Hot Spots Near the Black Hole Horizon of Sgr A* at Radio and Near-Infrared Wavelengths
• Evidence for Spin and Energy Extraction in a Galactic Black Hole Candidate: The XMM-Newton/EPIC-pn Spectrum of XTE J1650-500
• Compton reflection and iron fluorescence in BeppoSAX observations of Seyfert type 1 galaxies
• A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei
• X-ray Spectroscopy of QSOs with Broad Ultraviolet Absorption Lines
• Imaging Bright Spots in the Accretion Flow Near the Black Hole Horizon of Sgr A*
• The Connection Between Radio Quiet AGN and the High/Soft State of X-Ray Binaries
• The Cores of the Fe K$\alpha$ Lines in Active Galactic Nuclei: an Extended Chandra High Energy Grating Sample
• The Cores of the Fe K Lines in Seyfert I Galaxies Observed by the Chandra High Energy Grating
• Long-Term X-ray Spectral Variability in Seyfert 1 Galaxies
• Resolving the Composite Fe K-alpha Emission Line in the Galactic Black Hole Cygnus X-1 with Chandra
• Evidence for Rapid Iron K_alpha Line Flux Variability in MCG--6-30-15
• X-Ray/Ultraviolet Observing Campaign of the Markarian 279 Active Galactic Nucleus Outflow: a close look at the absorbing/emitting gas with Chandra-LETGS
• Fe K Emission and Absorption in the XMM-EPIC Spectrum of the Seyfert Galaxy IC 4329a
• X-ray reprocessing in Seyfert Galaxies: simultaneous XMM-Newton/BeppoSAX observations
• Chandra High Energy Grating Observations of the Fe Ka Line Core in Type 2 Seyfert Galaxies: A Comparison with Type 1 Nuclei
• Fe XXV and Fe XXVI Diagnostics of the Black Hole and Accretion Disk in Active Galaxies: Chandra Time-Resolved Spectroscopy of NGC 7314
• X-ray absorption lines suggest matter infalling onto the central black-hole of Mrk 509
• The Kinematics and Physical Conditions of the Ionized Gas in Markarian 509. I. Chandra High-Energy Grating Spectroscopy
• Gemini/GMOS IFU stellar kinematics of the nuclear region of six nearby active galaxies
• Revisiting The Spectral and Timing Properties of NGC 4151
• The structure and radiation spectra of illuminated accretion disks in AGN. II. Flare/spot model of X-ray variability
• A Relativistic Fe K-alpha Emission Line in the Intermediate Luminosity BeppoSAX Spectrum of the Galactic Microquasar V4641 Sgr
• Characterising the complex absorber in NGC 4151
• The Seyfert-Starburst Connection in X-rays. I. The Data
• X-ray spectral variability of the Seyfert galaxy NGC 4051
• High resolution X-ray spectroscopy of the Seyfert 1 Mrk841: insights into the warm absorber and warm emitter
• The Compton shoulder of the Fe Kalpha fluorescent emission line in active galactic nuclei
• NGC 4151: an intrinsically average Seyfert 1
• Intrinsic Absorption in the Spectrum of Mrk 279: Simultaneous Chandra, FUSE, and STIS Observations
• X-ray spectral properties of Seyfert galaxies and the unification scheme
• Iron K Features in the Quasar E 1821+643: Evidence for Gravitationally Redshifted Absorption?
• On the nuclear obscuration of H2O maser galaxies
• Unveiling the AGN powering the "Composite" Seyfert/Star-forming galaxy NGC 7679: BeppoSAX and ASCA results
• Chandra High-Resolution X-ray Spectroscopy of the Fe K Line in the Seyfert 1 Galaxy NGC 3783
• The XMM-Newton RGS spectrum of the high luminosity Seyfert 1 galaxy Markarian 509
• The response of the Fe Kαline to changes in the X-ray illumination of accretion discs
• On the contribution of microlensing to X-ray variability of high-redshifted QSOs
• XMM-Newton RGS observation of the warm absorber in Mrk 279
• X-ray Reflection from Inhomogeneous Accretion Disks: I. Toy Models and Photon Bubbles
• On the X-ray Baldwin Effect in Active Galactic Nuclei Observed by the Chandra High Energy Grating
• The X-ray Properties of Active Galactic Nuclei with Double-Peaked Balmer Lines
• Reprocessing of X-rays in AGN. I. Plane parallel geometry -- test of pressure equilibrium
• On the variability of the iron line in Mrk 841
• An X-ray Spectral Analysis of the Central Regions of NGC 4593
• XMM-Newton unveils the complex iron K alpha region of Mrk 279
• Monte Carlo simulations of the Nickel K$\alpha$ fluorescent emission line in a toroidal geometry
• Testing General Relativity with High-Resolution Imaging of Sgr A*
• X-ray Reflection from Inhomogeneous Accretion Disks: II. Emission Line Variability and Implications for Reverberation Mapping
• The kpc Scale Fe K$\alpha$ Emission in the Compton Thin Seyfert 2 Galaxy NGC 4388 resolved by Chandra
• Short Timescale Correlations Between Line and Continuum Fluxes in Cygnus X-1
• A Suzaku Observation of MCG-2-58-22: Constraining the Geometry of the Circumnuclear Material
• Does the Iron K${}_{\alpha }$ Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?
• Possible X-ray diagnostic for jet/disk dominance in Type 1 AGN
• The Correlation between X-ray spectral slope and FeKalpha line energy in radio-quiet active galactic nuclei
• On the equivalent width of the Fe K$\alpha$ line produced by a dusty absorber in active galactic nuclei
• Broadband spectral analysis of Mrk 926 using multi-epoch X-ray observations
• Detection of Asymmetry in the Narrow Fe K$\alpha$ Emission Line in MCG-5-23-16 with Chandra