2004MNRAS.350L..26N

We propose a new method of estimation of the black hole masses in active galactic nuclei (AGN) based on the normalized excess variance, σ²_nxs. We derive a relation between σ²_nxs, the length of the observation, T, the light-curve bin size, Δt, and the black hole mass, assuming that (I) the power spectrum above the high-frequency break, ν_bf, has a slope of -2, (II) the high-frequency break scales with black hole mass, (III) the power-spectrum amplitude (in frequency-power space) is universal and (iv) σ²_nxsis calculated from observations of length T < 1/ν_bf. Values of black hole masses in AGN obtained with this method are consistent with estimates based on other techniques such as reverberation mapping or the M_BH-stellar velocity dispersion relation. The method is formally equivalent to methods based on power spectrum scaling with mass, but the use of σ²_nxshas the big advantage of being applicable to relatively low-quality data.