2005AJ....130.2506X

We have spectrophotometrically observed a sample of five optically violently variable quasars, for which short-timescale optical variabilities have been observed during our optical monitoring campaign since 1994. Using the relationship between black hole masses and optical continuum luminosity at the rest wavelength of 5100 Å, we derived the central black hole masses, M_BH. We also estimated the relevant black hole masses, M_H, using rapid-variability timescales and our new formula for black hole mass estimates. The differences logM_BH/M_Hare limited by|logM_BH/M_H|≤0.62, which implies that the two methods of estimating black hole masses by the rapid-variability timescales and the reverberation mapping method should be reliable. We also discuss the origin of the double-peaked Hβ emission line in PKS 1510-089 and show it to be probable that the double-peaked Hβ emission line is mainly produced by a nonaxisymmetric accretion disk surrounding the central Kerr black hole.