Abstract
Abstract Many Seyfert galaxies are known to exhibit significant X-ray spectral variations and seemingly broad iron K-emission line features. In this paper, we show that the “variable partial covering model,” which has been successfully proposed for MCG −6–30–15 (Miyakawa et al. 2012, PASJ, 64, 140) and 1H 0707−495 (Mizumoto et al. 2014, PASJ, 66, 122), can also explain the spectral variations in 2–10 keV as well as the broad iron line features in 20 other Seyfert galaxies observed with Suzaku. In this model, the absorbed spectral component through the optically thick absorbing clouds has a significant iron K-edge, which primarily accounts for the observed, seemingly broad iron line feature. Fluctuation of the absorbing clouds in the line of sight of the extended X-ray source results in variation of the partial covering fraction, which causes an anti-correlation between the direct (not covered) spectral component and the absorbed (covered) spectral component below ∼10 keV. Observed spectral variation in 2–10 keV in a timescale of less than ∼1 day is primarily explained by such variations of the partial covering fraction, while the intrinsic soft X-ray luminosity is hardly variable.
Highlights
Significant and aperiodic X-ray variation is one of the main characteristics of the ActiveGalactic Nuclei (AGN)
We have seen that the Variable Partial Covering (VPC) model, which has been proposed for MCG-6-30-15 (MEI2012) and 1H0707–495 (MES2014), can explain the 2–10 keV spectral variation of 20 other Seyfert galaxies observed with Suzaku
We propose that observed X-ray flux/spectral variation of Seyfert galaxies is explained by variation of the partial covering fraction in timescales below
Summary
Significant and aperiodic X-ray variation is one of the main characteristics of the ActiveGalactic Nuclei (AGN). MCG-6-30-15 is a representative example; its iron emission line profile seems to be broadened and skewed (e.g., Tanaka et al 1995), and fractional variation of the energy spectrum significantly drops at the iron line energy band (Fabian et al.2002; Matsumoto et al 2003). A possible scenario to explain these phenomena is the “lightbending model”. In this model, the fluorescent iron line is emitted at the innermost part of the accretion disk, so that the line profile is broadened and skewed, and the disk-reflected photons are much less variable than the direct photons due to relativistic reverberation (Fabian and Vaughan 2003; Miniutti & Fabian 2004). The seemingly broad iron emission line feature may be interpreted due to iron K-edge feature caused by partial covering of the central
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