Quasar Black Hole Mass Estimates in the Era of Time Domain Astronomy
  We investigate the dependence of the normalization of the high-frequency part
of the X-ray and optical power spectral densities (PSD) on black hole mass for
a sample of 39 active galactic nuclei (AGN) with black hole masses estimated
from reverberation mapping or dynamical modeling. We obtained new Swift
observations of PG 1426+015, which has the largest estimated black hole mass of
the AGN in our sample. We develop a novel statistical method to estimate the
PSD from a lightcurve of photon counts with arbitrary sampling, eliminating the
need to bin a lightcurve to achieve Gaussian statistics, and we use this
technique to estimate the X-ray variability parameters for the faint AGN in our
sample. We find that the normalization of the high-frequency X-ray PSD is
inversely proportional to black hole mass. We discuss how to use this scaling
relationship to obtain black hole mass estimates from the short time-scale
X-ray variability amplitude with precision ~ 0.38 dex. The amplitude of optical
variability on time scales of days is also anti-correlated with black hole
mass, but with larger scatter. Instead, the optical variability amplitude
exhibits the strongest anti-correlation with luminosity. We conclude with a
discussion of the implications of our results for estimating black hole mass
from the amplitude of AGN variability.
