Suzaku Results on the Obscured Low-Luminosity Active Galactic Nucleus in NGC 4258

TL;DR

This study used Suzaku observations to analyze the obscured low-luminosity active galactic nucleus in NGC 4258, revealing spectral properties, variability, and the nature of surrounding material, suggesting a localized cold reflector rather than a thick torus.

Contribution

First Suzaku-based detailed spectral analysis of NGC 4258's low-luminosity AGN, providing insights into its obscuring material and nuclear environment.

Findings

Detected X-ray variability by a factor of 2 during observation.

Found no need for a cold reflection component, indicating a localized reflector.

Measured a weak Fe-Kalpha line with an equivalent width of ~40 eV.

Abstract

In 2006 June, the obscured low luminosity active galactic nucleus in the nearby Seyfert 1.9 galaxy NGC 4258 was observed with Suzaku for ~ 100 ks. Utilizing the XIS and the HXD, the nucleus emission was detected over 2 to 40 keV range, with an unabsorbed 2--10 keV luminosity of 8 x 10 40 erg / s, and varied by a factor of ~ 2 during the observation. Its 2--40 keV spectrum is reproduced by a single power law with photon index of ~ 2.0, absorbed by an equivalent hydrogen column of ~ 1.0 x 10 23 cm2. The spectrum within 4' of the nucleus required also a softer thin-thermal emission, as well as an intermediate hardness component attributable to integrated point sources. A weak neutral Fe-Kalpha florescence line was detected at an equivalent width of ~ 40 eV. The cold reflection component was not required by the data, with the reflector solid angle Omega seen from the nucleus constrained as Omega / 2 pi < 0.3 assuming a general case of 60 deg inclination. The results suggest that the cold reflecting material around the nucleus is localized along our line of sight, rather than forming a thick torus.