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

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

Sep 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...414l..85l&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 414, no. 2, p. L85-L88.

Astronomy and Astrophysics

Astrophysics

123

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

Scientific paper

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.

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