Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observations

Abstract

[abridged] We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT survey. We find that signatures of X-ray reprocessing by cold gas are very weak in the spectrum of this Seyfert-2 galaxy; a weak, narrow fluorescent-Kalpha emission line of cold iron is robustly detected in both the Suzaku and XMM-Newton spectra but at a level much below that of most other Seyfert-2 galaxies. We conclude that the circumnuclear environment of this AGN is very "clean" and lacks the Compton-thick obscuring torus of unified Seyfert schemes. From the narrowness of the iron line, together with evidence for line flux variability between the Suzaku and XMM-Newton observations, we constrain the line emitting region to be between $3\times 10^3{r}_g$ and $4\times 10^4{r}_g$ from the black hole. We show that the observed properties of the iron line can be explained if the line originates from the surface layers of a warped accretion disk. In particular, we present explicit calculations of the expected iron line from a disk warped by Lens-Thirring precession from a misaligned central black hole. Finally, the Suzaku data reveal clear evidence for large amplitude 2-10keV variability on timescales of 50ksec as well as smaller amplitude flares on timescales as short as 5-10ksec. If associated with accretion disk processes, such rapid variability requires an origin in the innermost regions of the disk ($r\approx 10r_g$ or less).

10 pages, 6 figures. Accepted for publication in the Astrophysical Journal

References in corpus (10)

• Constraining Black Hole Spin Via X-ray Spectroscopy
• Swift BAT Survey of AGN
• X-ray Spectral Properties of the BAT AGN Sample
• The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258
• Seyfert galaxies in the local Universe (z$\le$ 0.1): the average X-ray spectrum as seen by $BeppoSAX$
• Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes
• Alignment and Precession of a Black Hole with a Warped Accretion Disc
• X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC 4258 from Weeks to Years
• The Warped Disc of NGC 4258
• Chandra X-ray Observations of NGC 4258: Iron Absorption Lines from the Nucleus

Cited by in corpus (24)

• Radiatively Inefficient Accretion in Nearby Galaxies
• The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation
• Relativistic Lines and Reflection from the Inner Accretion Disks Around Neutron Stars
• A global view of the inner accretion and ejection flow around super massive black holes: radiation driven accretion disk winds in a physical context
• Truncation of the Inner Accretion Disk around a Black Hole at Low Luminosity
• Chandra High Energy Grating Observations of the Fe Ka Line Core in Type 2 Seyfert Galaxies: A Comparison with Type 1 Nuclei
• Are X-ray Emitting Coronae around Super Massive Black Holes Outflowing?
• Assessing black hole spin in deep Suzaku observations of Seyfert 1 AGN
• Detection of jet precession in the active nucleus of M81
• Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C390.3
• The variable and non-variable X-ray absorbers in Compton-thin type-II Active Galactic Nuclei
• Study of Swift/BAT Selected Low-luminosity Active Galactic Nuclei Observed with Suzaku
• Millimeter Radio Continuum Emissions as the Activity of Super Massive Black Holes in Nearby Early-Type Galaxies and Low-Luminosity Active Galactic Nuclei
• Infalling clouds onto super-massive black hole binaries - I. Formation of discs, accretion and gas dynamics
• Exploring Accretion and Disk-Jet Connections in the LLAGN M81*
• The Dynamics of Truncated Black Hole Accretion Disks II: Magnetohydrodynamic Case
• Gamma-ray activity of Seyfert galaxies and constraints on hot accretion flows
• Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift
• Warping of accretion disk and launching of jet by a spinning black hole in NGC 4258
• Suzaku Observation of the Metallicity in the Interstellar Medium of NGC 4258
• The flare model for X-ray variability of NGC 4258
• A comprehensive X-ray view of the active nucleus in NGC 4258
• Hot accretion flows in low-luminosity active galactic nuclei in NGC 4258 and NGC 7213
• A truncated inner disc in the Seyfert 1 galaxy WKK 4438