On the Nature of X-ray Variability in Ark 564

Abstract

We use data from a recent long ASCA observation of the Narrow Line Seyfert 1 Ark 564 to investigate in detail its timing properties. We show that a thorough analysis of the time series, employing techniques not generally applied to AGN light curves, can provide useful information to characterize the engines of these powerful sources.We searched for signs of non-stationarity in the data, but did not find strong evidences for it. We find that the process causing the variability is very likely nonlinear, suggesting that variability models based on many active regions, as the shot noise model, may not be applicable to Ark 564. The complex light curve can be viewed, for a limited range of time scales, as a fractal object with non-trivial fractal dimension and statistical self-similarity. Finally, using a nonlinear statistic based on the scaling index as a tool to discriminate time series, we demonstrate that the high and low count rate states, which are indistinguishable on the basis of their autocorrelation, structure and probability density functions, are intrinsically different, with the high state characterized by higher complexity.

13 pages, 13 figures, accepted for publication in A&A

References in corpus (7)

• X-ray Spectral Variability and Rapid Variability of the Soft X-ray Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180
• The Fragmentation of Pre-enriched Primordial Objects
• Variability Time Scales of TeV Blazars Observed in the ASCA Continuous Long-Look X-ray Monitoring
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• Detection of a high frequency break in the X-ray power spectrum of Ark 564
• XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504
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• The Variability of the Narrow-line Seyfert 1 Galaxies from the PanSTARRS's View
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