An X-ray view of the active nucleus in NGC 4258

Abstract

XMM-Newton observed the Seyfert 1.9 galaxy NGC 4258 in December 2000. At energies above 2 keV a hard nuclear point source is resolved that can be fitted by a highly absorbed power-law spectrum (NH = (8.0+-0.4)x10^22 cm^-2, photon index 1.64+-0.08) with an unabsorbed luminosity of 7.5x10^40erg/s in the 2-10 keV band. No narrow iron Kalpha emission line is detected (90% upper limit of equivalent width EW ~40 eV). The nuclear emission flux was observed to remain constant over the observation. A short archival Chandra observation taken in March 2000 further constrains the hard emission to a point source coincident with the radio nucleus. A point source ~3" southwest of the nucleus does not contribute significantly. Spectral results of the Chandra nuclear source are comparable (within the limited statistics) to the XMM-Newton parameters. The comparison of our iron line upper limit with reported detections indicates variability of the line EW. These results can be explained by the relatively low nuclear absorption of NGC 4258 (which is in the range expected for its intermediate Seyfert type) and some variability of the absorbing material. Reflection components as proposed to explain the large iron line EW of highly absorbed Seyfert 2 galaxies and/or variations in the accretion disk are however imposed by the time variability of the iron line flux.

arXiv comment6 pages, 5 figures, accepted for publication in A&A

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• Chandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M 106)
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Cited by in corpus (15)

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• Low-Luminosity Active Galactic Nuclei: Are They UV-Faint and Radio Loud?
• Extragalactic H_2O masers and X-ray absorbing column densities
• NGC4258: a jet-dominated low-luminosity AGN?
• Probing the Magnetic Field at Sub-Parsec Radii in the Accretion Disk of NGC 4258
• X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC 4258 from Weeks to Years
• Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observations
• Low-Luminosity AGN as analogues of Galactic Black Holes in the low/hard state: Evidence from X-ray timing of NGC 4258
• Spatially resolved X-ray spectra of NGC 4258
• Chandra X-ray Observations of NGC 4258: Iron Absorption Lines from the Nucleus
• Suzaku Results on the Obscured Low-Luminosity Active Galactic Nucleus in NGC 4258
• XMM-Newton Observations of Luminous Sources in the Nearby Galaxies: NGC 4395, NGC 4736, and NGC 4258
• The flare model for X-ray variability of NGC 4258
• A comprehensive X-ray view of the active nucleus in NGC 4258