Revealing the X-ray Variability of AGN with Principal Component Analysis

Abstract

We analyse a sample of 26 active galactic nuclei with deep XMM-Newton observations, using principal component analysis (PCA) to find model independent spectra of the different variable components. In total, we identify at least 12 qualitatively different patterns of spectral variability, involving several different mechanisms, including five sources which show evidence of variable relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, NGC 3516 and Mrk 766) and three which show evidence of varying partial covering neutral absorption (NGC 4395, NGC 1365, and NGC 4151). In over half of the sources studied, the variability is dominated by changes in a power law continuum, both in terms of changes in flux and power law index, which could be produced by propagating fluctuations within the corona. Simulations are used to find unique predictions for different physical models, and we then attempt to qualitatively match the results from the simulations to the behaviour observed in the real data. We are able to explain a large proportion of the variability in these sources using simple models of spectral variability, but more complex models may be needed for the remainder. We have begun the process of building up a library of different principal components, so that spectral variability in AGN can quickly be matched to physical processes. We show that PCA can be an extremely powerful tool for distinguishing different patterns of variability in AGN, and that it can be used effectively on the large amounts of high-quality archival data available from the current generation of X-ray telescopes.

25 pages, 27 figures, accepted to MNRAS. Analysis code available on request to lead author. Edit: Rogue table removed

References in corpus (16)

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• An absorption origin for the X-ray spectral variability of MCG-6-30-15
• XMM-Newton study of the complex and variable spectrum of NGC 4051
• X-ray Absorption and Reflection in Active Galactic Nuclei
• The NuSTAR spectrum of Mrk 335: Extreme relativistic effects within 2 gravitational radii of the event horizon?
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• NuSTAR and XMM-Newton Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk
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• XMM-Newton observations of the Narrow-Line Seyfert 1 galaxy Mrk 335 in an historical low X-ray flux state
• The Variable X-ray Spectrum of Markarian 766 - II. Time-Resolved Spectroscopy
• Suzaku Studies of the Central Engine in the Typical Type I Seyfert NGC 3227: Detection of Multiple Primary X-ray Continua with Distinct Properties
• The NeXT Mission
• PCA of PCA: Principal Component Analysis of Partial Covering Absorption in NGC 1365
• Suzaku Discovery of a Slowly Varying Hard X-ray Continuum from the Type I Seyfert Galaxy NGC 3516

Cited by in corpus (14)

• Accretion disks and coronae in the X-ray flashlight
• Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712
• Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1
• Using principal component analysis to understand the variability of PDS 456
• The nature of the extreme X-ray variability in the NLS1 1H 0707-495
• A statistical study of the optical spectral variability in gamma-ray blazars
• X-ray flaring in PDS 456 observed in a high-flux state
• Ejection-accretion connection in NLS1 AGN 1H 1934-063
• The nature of the broadband X-ray variability in the dwarf Seyfert galaxy NGC 4395
• The nature of X-ray spectral variability in MCG-6-30-15
• Modelling X-ray RMS spectra II: the ultra-fast outflow of PDS 456
• X-ray Eclipses of Active Galactic Nuclei
• A Systematic Study of the Short-Term X-ray Variability of Seyfert Galaxies I. Diversity of the X-ray Rms Spectra
• The broad band SEDs of four 'hypervariable' AGN