Robotic Reverberation Mapping of the Southern Seyfert NGC 3783
  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 H$\beta$, HeII $\lambda 4686$,
H$\gamma$, and H$\delta$. From the time delay in the broad H$\beta$ emission
line and the line width in the variable portion of the spectrum, we derive a
black hole mass of $M_{\rm BH} = 2.34^{+0.43}_{-0.43} \times 10^7$ M$_{\odot}$.
This is slightly smaller than, but consistent with, previous determinations.
However, our significantly improved time sampling ($T_{\rm med}=1.7$ days
compared to $T_{\rm med}=4.0$ days) has reduced the uncertainties on both the
time delay and the derived mass by $\sim 50$%. We also detect clear
velocity-resolved time delays across the broad H$\beta$ 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 AGNs for which we have direct, primary black hole mass measurements.
Upcoming MUSE observations at VLT 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.
