X-ray variability of active galactic nuclei - A universal power spectrum with luminosity-dependent amplitude

A. Lawrence, I. Papadakis

Research output: Contribution to journalArticlepeer-review

Abstract

We present power-law model fits to the power spectra of 12 high-quality 'long look' observations of AGNs from the EXOSAT data base. The AGN concerned differ in X-ray luminosity L(x) over a range 10,000. The results are consistent with all objects having a power spectrum index equal to the mean value alpha = 1.55. There is no correlation with L(x) suggesting that the power spectrum has little curvature over many decades of frequency. The mean slope is inconsistent with both standard shot-noise processes and traditional '1/f noise' but close to the prediction of simple 'rotating hot spot' models. The power spectrum amplitude shows large object-to-object scatter but varies systematically as L(x) exp -0.5. This is inconsistent with any fixed-shape shot-noise model. Given the mean power spectrum slope, we then deduce that the time scale which gives fixed power spectral density varies as approximately L(x) exp 0.3; however, the time scale below which there is fixed integrated power varies almost exactly linearly with luminosity.
Original languageEnglish
JournalAstrophysical Journal
Volume414
DOIs
Publication statusPublished - 1 Sep 1993

Keywords

  • Galactic Nuclei
  • Luminosity
  • Power Spectra
  • Seyfert Galaxies
  • X Ray Spectra
  • Astronomical Models
  • Exosat Satellite
  • Light Curve
  • Time Series Analysis

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