NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-17 T12:24:47 PDT
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For refcode 1993ApJ...414L..85L:
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1993ApJ...414L..85L X-RAY VARIABILITY OF ACTIVE GALACTIC NUCLEI: A UNIVERSAL POWER SPECTRUM WITH LUMINOSITY-DEPENDENT AMPLITUDE A. LAWRENCE AND I. PAPADAKIS Physics Department, Queen Mary and Westfield College, Mile End Road, London El 4N5 England Received 1993 January 27; accepted 1993 June 3 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 AGNs concerned differ in X-ray luminosity L_x_, over a range 10^4^. 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 "l/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_^-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 ~L_x_^0.3^; however, the time scale below which there is fixed integrated power varies almost exactly linearly with luminosity. Subject headings: galaxies: Seyfert - quasars: general - X-rays: galaxies
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