A comprehensive X-ray view of the active nucleus in NGC 4258

Abstract

(Abridged) We present a detailed broadband X-ray spectrum of NGC 4258, with the goal of precisely measuring the coronal luminosity and accretion flow properties of the AGN, and track any possible variation across two decades of observations. We collect archival XMM-Newton, Chandra, Swift/BAT and NuSTAR spectroscopic observations spanning 15 years, and fit them with a suite of state of the art models, including a warped disk model which is suspected to provide the well known obscuration observed in the X-rays. We complement this information with archival results from the literature. Clear spectral variability is observed among the different epochs. The obscuring column density shows possibly periodic fluctuations on a timescale of 10 years, while the intrinsic luminosity displays a long term decrease of a factor of three in a time span of 15 years (from $L_{2-10\text{keV}}\sim 10^{41}$ erg s${}^{-1}$ in the early 2000s, to $L_{2-10\text{keV}}\sim 3\times 10^{40}$ erg s${}^{-1}$ in 2016). The average absorption-corrected X-ray luminosity $L_{2-10\text{keV}}$, combined with archival determinations of the bolometric luminosity, implies a bolometric correction $k_{\mathrm{bol}}\sim 20$, intriguingly typical for Seyferts powered by accretion through geometrically thin, radiatively efficient disks. Moreover, the X-ray photon index $\Gamma$ is consistent with the typical value of the broader AGN population. However, the accretion rate in Eddington units is very low, well within the expected RIAF regime. Our results suggest that NGC 4258 is a genuinely low-luminosity Seyfert II, with no strong indications in its X-ray emission for a hot, RIAF-like accretion flow.

arXiv commentAccepted for publication in A&A. 14 pages, 6 figures, 3 tables

References in corpus (57)

• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Advection-Dominated Accretion: Underfed Black Holes and Neutron Stars
• The Burst Alert Telescope (BAT) on the Swift MIDEX Mission
• On the Fate of Gas Accreting at a Low Rate onto a Black Hole
• Magnetically Arrested Disk: An Energetically Efficient Accretion Flow
• The Stellar Cusp Around the Supermassive Black Hole in the Galactic Center
• BAT AGN Spectroscopic Survey - V. X-ray properties of the Swift/BAT 70-month AGN catalog
• An X-ray Spectral Model for Compton-Thick Toroidal Reprocessors
• Bolometric luminosities and Eddington ratios of X-ray selected Active Galactic Nuclei in the XMM-COSMOS survey
• The 105 month Swift-BAT all-sky hard X-ray survey
• The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints
• Universal bolometric corrections for AGN over 7 luminosity decades
• An XMM-Newton spectral survey of 12 micron selected galaxies. I. X-ray data
• Toward a New Geometric Distance to the Active Galaxy NGC 4258. III. Final Results and the Hubble Constant
• An Improved Distance to NGC 4258 and its Implications for the Hubble Constant
• Calibration of the NuSTAR High Energy Focusing X-ray Telescope
• The Megamaser Cosmology Project. III. Accurate Masses of Seven Supermassive Black Holes in Active Galaxies with Circumnuclear Megamaser Disks
• New Spectral Model for Constraining Torus Covering Factors from Broadband X-ray Spectra of Active Galactic Nuclei
• A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys
• The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation
• Is the Accretion Flow in NGC 4258 Advection-dominated?
• The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258
• X-ray Properties of LINERs and Low-luminosity Seyfert Galaxies Observed with ASCA. I. Observations and Results
• Spectral Models for Low-luminosity Active Galactic Nuclei in LINERs: The Role of Advection-dominated Accretion and Jets
• NuSTAR Spectroscopy of Multi-Component X-ray Reflection from NGC 1068
• The anti-correlation between the hard X-ray photon index and the Eddington ratio in LLAGNs
• The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
• Study on X-ray Spectra of Obscured AGNs based on Monte Carlo simulation - an interpretation of observed wide-band spectra
• The Swift/BAT AGN Spectroscopic Survey (BASS) -- VI. The Gamma_X - L/L_Edd relation
• IACHEC Cross-Calibration of Chandra, NuSTAR, Swift, Suzaku, and XMM-Newton with 3C 273 and PKS 2155-304
• What is the Accretion Rate in NGC 4258?
• Toward a New Distance to the Active Galaxy NGC 4258: II. Centripetal Accelerations and Investigation of Spiral Structure
• The variable hard X-ray emission of NGC4945 as observed by NuSTAR
• The Megamaser Cosmology Project. VI. Observations of NGC 6323
• NGC4258: a jet-dominated low-luminosity AGN?
• NuSTAR observations of water megamaser AGN
• VLBA Continuum Observations of NGC 4258: Constraints on an Advection-Dominated Accretion Flow
• NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei: II. Median High-energy Cutoff in Seyfert II Hard X-ray Spectra
• Optical Detection of the Hidden Nuclear Engine in NGC~4258
• Chandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M 106)
• High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258
• Study of Swift/BAT Selected Low-luminosity Active Galactic Nuclei Observed with Suzaku
• A deep X-ray observation of NGC 4258 and its surrounding field
• X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC 4258 from Weeks to Years
• Physically motivated X-ray obscurer models
• A growth-rate indicator for Compton-thick active galactic nuclei
• Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observations
• Radiative Properties of Magnetically-Arrested Disks
• The BeppoSAX view of the X-ray active nucleus of NGC4258
• Reflection geometries in absorbed and unabsorbed AGN
• Jet-Shocked H2 and CO in the Anomalous Arms of Molecular Hydrogen Emission Galaxy NGC 4258
• An X-ray view of the active nucleus in NGC 4258
• Chandra X-ray Observations of NGC 4258: Iron Absorption Lines from the Nucleus
• Warping of accretion disk and launching of jet by a spinning black hole in NGC 4258
• Observational hints on the torus obscuring gas behaviour through X-rays with NuSTAR data
• Measuring the Obscuring Column of a Disk Megamaser AGN in a Nearby Merger

Cited by in corpus (1)

• Hot accretion flows in low-luminosity active galactic nuclei in NGC 4258 and NGC 7213