Simple interpretation of the seemingly complicated X-ray spectral variation of NGC 5548

Abstract

NGC 5548 is a very well-studied Seyfert 1 galaxy in broad wavelengths. Previous multiwavelength observation campaigns have indicated that its multiple absorbers are highly variable and complex. A previous study applied a two-zone partial covering model with different covering fractions to explain the complex X-ray spectral variation and reported a correlation between one of the covering fractions and the photon index of the power-law continuum. However, it is not straightforward to physically understand such a correlation. In this paper, we propose a model to avoid this unphysical situation; the central X-ray emission region is partially covered by clumpy absorbers composed of double layers. These "double partial coverings" have precisely the same covering fraction. Based on our model, we have conducted an extensive spectral study using the data taken by XMM-Newton, Suzaku, and NuSTAR in the range of 0.3-78 keV for 16 years. Consequently, we have found that the X-ray spectral variations are mainly explained by independent changes of the following three components; (1) the soft excess spectral component below ~1 keV, (2) the cut-off power-law normalization, and (3) the partial covering fraction of the clumpy absorbers. In particular, spectral variations above ~1 keV are mostly explained only by the changes of the partial covering fraction and the power-law normalization. In contrast, the photon index and all the other spectral parameters are not significantly variable.

14 pages, 13 figures, Published in MNRAS

References in corpus (17)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• An XMM-Newton survey of broad iron lines in Seyfert galaxies
• A fast and long-lived outflow from the supermassive black hole in NGC 5548
• Space Telescope and Optical Reverberation Mapping Project. I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 with the Cosmic Origins Spectrograph on Hubble Space Telescope
• IACHEC Cross-Calibration of Chandra, NuSTAR, Swift, Suzaku, and XMM-Newton with 3C 273 and PKS 2155-304
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
• Chasing obscuration in type-I AGN: discovery of an eclipsing clumpy wind at the outer broad-line region of NGC 3783
• Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical Nature of the Outflow from HST/COS Observations
• The origin of ultra-fast outflows in AGN: Monte-Carlo simulations of the wind in PDS 456
• On the Observational Difference Between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei
• Stratified disc wind models for the AGN broad-line region: ultraviolet, optical and X-ray properties
• Anatomy of the AGN in NGC 5548: III. The high-energy view with NuSTAR and INTEGRAL
• X-ray spectroscopic survey of highly-accreting AGN
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system III. Dipping in the low/hard state
• Interpretation of the X-ray Spectral Variation of 1H0707-495 with a Variable Double Partial Covering Model
• Nature of the Warm Absorber Outflow in NGC 4051
• Origin of the Characteristic X-ray Spectral Variations of IRAS 13224$-$3809

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