Interpretation of the X-ray Spectral Variation of 1H0707-495 with a Variable Double Partial Covering Model

TL;DR

This paper explains the X-ray spectral variations of galaxy 1H0707-495 using a variable double partial covering model involving ionized absorption layers, revealing that spectral changes are mainly due to covering fraction variations.

Contribution

The study introduces a novel variable double partial covering model that accounts for spectral variations without significant changes in intrinsic luminosity or shape.

Findings

Spectral variations are primarily due to changes in partial covering fraction.

Intrinsic luminosity and spectral shape are stable over a day.

Different timescales govern intrinsic luminosity and covering fraction changes.

Abstract

The Narrow-line Seyfert 1 galaxy 1H0707-495 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 1H0707-495 in 0.5-10 keV is successfully explained by a "variable double partial covering model" where the original continuum spectrum, which is composed of the soft multi-color disk blackbody component and the 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 a ~ day is mostly explained by only variation of the partial covering fraction. In our model, the intrinsic luminosity and spectral shape are hardly variable within a ~ day, 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 in this timescale, and the hard power-law component is more variable. We propose that the observed spectral variation of 1H0707-495 is caused by three physically independent variations with different timescales; (1) intrinsic luminosity variation over days, (2) variation of partial covering fraction at a timescale of hours, and (3) small intrinsic hard component variation above 3 keV in a timescale of hours or less.