Interpretation of the X-ray spectral variation of 1H 0707-495 with a variable double partial covering model

Abstract

The narrow-line Seyfert 1 galaxy 1H 0707-495 is known to exhibit significant X-ray spectral variations. Its X-ray energy spectrum is characterized by a strong soft excess emission, an extremely deep iron K-edge structure at ∼ 7 keV, and a putative iron L-line/edge feature at ∼ 1 keV. We have found that the energy spectrum of 1H 0707-495 in 0.5-10 keV is successfully explained by a "variable double partial covering model" where the original continuum spectrum, which is composed of a soft multi-color disk blackbody component and a hard power-law component, is partially covered by two ionized absorption layers with different ionization states and the same partial covering fraction. The lower-ionized and thicker absorption layer primarily explains the iron K-edge feature, and the higher-ionized and thinner absorption layer explains the L-edge feature. We have discovered that the observed significant intensity/spectral variation within ∼ 1 d is mostly explained by varying only the partial covering fraction. In our model, the intrinsic luminosity and spectral shape are hardly variable within ∼ 1 d, while some intrinsic variability above 3 keV is recognized. This is consistent with the picture that the multi-color disk blackbody spectrum is almost invariable on this timescale, and the hard power-law component is more variable. We propose that the observed spectral variation of 1H 0707-495 is caused by three physically independent variations with different timescales; (1) intrinsic luminosity variation over days, (2) variation of partial covering fraction on a timescale of hours, and (3) small intrinsic hard component variation above 3 keV on a timescale of hours or less.