We have undertaken a new ground-based monitoring campaign to improve the estimates of the mass of the central black hole in NGC 4151. We measure the lag time of the broad H line response compared to the optical continuum at 5100 8 and find a lag of 6:6 þ1:1 À0:8 days. We combine our data with the recent reanalysis of UVemission lines by Metzroth and coworkers to calculate a weighted mean of the black hole mass, M BH ¼ (4:57 þ0:57 À0:47 ) ; 10 7 M . The absolute calibration of the black hole mass is based on normalization of the AGN black hole mass-stellar velocity dispersion (M BH -Ã ) relationship to that of quiescent galaxies by Onken and coworkers. The scatter in the M BH -Ã relationship suggests that reverberation-mapping-based mass measurements are typically uncertain by a factor of 3Y4.

We present results of an intensive 2 month campaign of ground-based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution day. The broad Ha and Hb emission [ 1 lines respond to D35% ultraviolet continuum variations with an amplitude of D10% and time delays of 5.6^1.3 days and 5.4^0.8 days, respectively. We interpret this as evidence of variable Balmer line gas D5È6 light days from the central source in this object, widely believed to be a supermassive black hole. The virial mass of the central source implied by line widths and time delays is D106È107 Concomi-M _. tantly, we Ðnd evidence for wavelength-dependent continuum time delays : optical continuum variations lag those at 1315 by 1.0^0.3 days at 4865 to 1.5^0.7 days at 6962 This suggests a stratiÐed A A A. continuum reprocessing region extending several light days from the central source, possibly an accretion disk.

We describe results from a new ground-based monitoring campaign on NGC 5548, the best studied reverberation-mapped AGN. We find that it was in the lowest luminosity state yet recorded during a monitoring program, namely L 5100 = 4.7 × 10 42 ergs s −1 . We determine a rest-frame time lag between flux variations in the continuum and the Hβ line of 6.3 +2.6 −2.3 days. Combining our measurements with those of previous campaigns, we determine a weighted black hole mass of M BH = 6.54 +0.26 −0.25 × 10 7 M ⊙ based on all broad emission lines with suitable variability data. We confirm the previously-discovered virial relationship between the time lag of emission lines relative to the continuum and the width of the emission lines in NGC 5548, which is the expected signature of a gravity-dominated broad-line region. Using this lowest luminosity state, we extend the range of the relationship between the luminosity and the time lag in NGC 5548 and measure a slope that is consistent with α = 0.5, the naive expectation for the broad line region for an assumed form of r ∝ L α . This value is also consistent with the slope recently determined by Bentz et al. for the population of reverberation-mapped AGNs as a whole.