2021ApJ...906...50B

We present spectroscopic and photometric monitoring of NGC 3783 conducted throughout the first half of 2020. Time delays between the continuum variations and the response of the broad optical emission lines were clearly detected, and we report reverberation measurements for Hβ, He II λ4686, Hγ, and Hδ. From the time delay in the broad Hβ emission line and the line width in the variable portion of the spectrum, we derive a black hole mass of M_BH=2.34_–0.43^+0.43×10⁷M_☉. This is slightly smaller than, but consistent with, previous determinations. However, our significantly improved time sampling (T_med = 1.7 days compared to T_med = 4.0 days) has reduced the uncertainties on both the time delay and the derived mass by ∼50%. We also detect clear velocity-resolved time delays across the broad Hβ profile, with shorter lags in the line wings and a longer lag in the line core. Future modeling of the full velocity-resolved time-delay response will further improve the reverberation-based mass for NGC 3783, adding it to the small but growing sample of active galactic nuclei for which we have constrained the black hole mass as well as the geometry and kinematics of the broad-ine region. Upcoming MUSE observations at the Very Large Telescope will also allow NGC 3783 to join the smaller sample of black holes where reverberation masses and masses from stellar dynamical modeling may be directly compared.