A variable partial covering model for the seyfert 1 galaxy mcg6-30-15

Abstract

We propose a simple spectral model for the Seyfert 1 Galaxy MCG6-30-15 that can explain most of the 1- 40 keV spectral variation by a change of the partial covering fraction, similar to that proposed by Miller, Turner, and Reeves (2008, A&A, 483, 437). Our spectral model is composed of three continuum components: (1) a direct powerlaw component, (2) a heavily absorbed power-law component by mildly ionized intervening matter, and (3) a colddisk reflection component far from the black hole with a moderate solid-angle (O=2'0.3) accompanying a narrow fluorescent iron line. The first two components are affected by the surrounding thin highly ionized absorber with NH ' 1023:4 cm-2 and log ̃' 3.4. The heavy absorber in the second component is fragmented into many clouds, each of which is composed of radial zones with different ionization states and different column densities, a main body (NH ' 1024:2 cm-2, log ̃' 1.6), an envelope (NH' 1022:1 cm-2, log ̃' 1.9), and presumably a completely opaque core. Not only the intrinsic spectral shape of the X-ray source but also these parameters of the ionized absorbers are unchanged at all. The central X-ray source extends moderately, and its luminosity is not significantly variable. The observed flux and spectral variations are mostly explained by the variation of the geometrical partial covering fraction of the central source ranging from 0 (uncovered) to 0.63 by the intervening ionized clouds in the line of sight. The ionized iron K-edge of the heavily absorbed component explains most of the seemingly broad linelike features, a well-known spectral characteristic of MCG6-30-15. The direct component and the absorbed one are negatively correlated, and their variations cancel out each other, so that the fractional spectral variation becomes the minimum at the iron-energy band; thus, another observational characteristic of MCG6-30-15 is explained. © 2012. Astronomical Society of Japan.