Estimating Black Hole Masses in Hundreds of Quasars
  We explore the practical feasibility of AGN broad-band reverberation mapping
and present first results. We lay out and apply a rigorous approach for
stochastic reverberation mapping of unevenly sampled multi-broad-band flux
measurements, assuming that the broad-line region (BLR) line flux is
contributing up to 15 % in some bands, and is directly constrained by one
spectroscopical epoch.
  The approach describes variations of the observed flux as the continuum,
modeled as a stochastic Gaussian process, and emission line contribution,
modeled as a scaled, smoothed and delayed version of the continuum. This
approach is capable not only to interpolate in time between measurements, but
also to determine confidence limits on continuum -- line emission delays. This
approach is applied to SDSS observations in 'Stripe 82' (S82) providing flux
measurements precise to 2 % at $\sim$ 60 epochs over $\sim$ 10 years. The
strong annual variations in the epoch sampling prove a serious limitation in
practice. Also, suitable redshift ranges must be identified, where strong broad
emission line contribute to one filter, but not to another.
  Through generating and evaluating problem-specific mock data, we verify that
S82-like data can constrain $\tau_{\mathrm{delay}}$ for a simple transfer
function model. In application to real data, we estimate
$\tau_{\mathrm{delay}}$ for 323 AGN with $0.225 < z < 0.846$, combining
information for different objects through the ensemble-scaling relationships
for BLR size and BH mass. Our analysis tentatively indicates a 1.7 times larger
BLR size of H$\alpha$ and MgII compared to Kaspi2000 and Vestergaard2002, but
the seasonal data sampling casts doubt on the robustness of the inference.
