2010ApJ...724...26M

We present the broadband X-ray power spectral density (PSD) function of the X-ray-luminous Seyfert 1.2 NGC 7469, measured from Rossi X-ray Timing Explorer monitoring data and two XMM-Newton observations. We find significant evidence for a turnover in the 2-10 keV PSD at a temporal frequency of 2.0^+3.0 _–0.8x10^–6 Hz or 1.0^+3.0_–0.6x 10^–6 Hz, depending on the exact form of the break (sharply broken or slowly bending power law, respectively). The "surrogate" Monte Carlo method of Press et al. was used to map out the probability distributions of PSD model parameters and obtain reliable uncertainties (68% confidence limits quoted here). The corresponding break timescale of 5.8±3.5 days or 11.6^+17.5_–8.7days, respectively, is consistent with the empirical relation between PSD break timescale, black hole mass, and bolometric luminosity of McHardy et al. Compared to the 2-10 keV PSD, the 10-20 keV PSD has a much flatter shape at high temporal frequencies, and no PSD break is significantly detected, suggesting an energy-dependent evolution not unlike that exhibited by several Galactic black hole systems.