Suzaku results on the obscured low-luminosity active galactic nucleus in NGC 4258

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 ̃ l00ks. Utilizing the XIS and the HXD, the nucleus emission was detected over a ̃2 to ̃40keV range, with an unabsorbed 2-10keV luminosity of ̃8 x 10 40ergs-1; it varied by a factor of ̃2 during the observation. Its 2-40 keV spectrum is reproduced by a single power law with a photon index of T ̃ 2.0, absorbed by an equivalent hydrogen column of ̃ 1.0 x 1023cm2. The spectrum within 4' of the nucleus also required a softer thin-thermal emission, as well as an intermediate hardness component, attributable to integrated point sources. A weak neutral Fe-Kα florescence line was detected at an equivalent width of ̃40eV. A cold reflection component was not required by the data, with the reflector solid angle f2 seen from the nucleus constrained as Sl/2n < 0.3, assuming a general case of 60° 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. © 2009 Astronomical Society of Japan.