  We present the broadband X-ray power spectral density function (PSD) 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,-0.8)e-6
Hz or 1.0(+3.0,-0.6)e-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. (1992) was used to map out the probability
distributions of PSD model parameters and obtain reliable uncertainties (68 per
cent confidence limits quoted here). The corresponding break time scale of 5.8
(+/- 3.5) days or 11.6(+17.5,-8.7) days, respectively, is consistent with the
empirical relation between PSD break time scale, 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.
