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We investigate the dependence of the normalization of the high-frequency partof the X-ray and optical power spectral densities (PSD) on black hole mass fora sample of 39 active galactic nuclei (AGN) with black hole masses estimatedfrom reverberation mapping or dynamical modeling. We obtained new Swiftobservations of PG 1426+015, which has the largest estimated black hole mass ofthe AGN in our sample. We develop a novel statistical method to estimate thePSD from a lightcurve of photon counts with arbitrary sampling, eliminating theneed to bin a lightcurve to achieve Gaussian statistics, and we use thistechnique to estimate the X-ray variability parameters for the faint AGN in oursample. We find that the normalization of the high-frequency X-ray PSD isinversely proportional to black hole mass. We discuss how to use this scalingrelationship to obtain black hole mass estimates from the short time-scaleX-ray variability amplitude with precision ~ 0.38 dex. The amplitude of opticalvariability on time scales of days is also anti-correlated with black holemass, but with larger scatter. Instead, the optical variability amplitudeexhibits the strongest anti-correlation with luminosity. We conclude with adiscussion of the implications of our results for estimating black hole massfrom the amplitude of AGN variability.

Quasar Black Hole Mass Estimates in the Era of Time Domain Astronomy