The Sloan Digital Sky Survey Reverberation Mapping Project: Comparison
  of Lag Measurement Methods with Simulated Observations
  We investigate the performance of different methodologies that measure the
time lag between broad-line and continuum variations in reverberation mapping
data using simulated light curves that probe a range of cadence, time baseline,
and signal-to-noise ratio in the flux measurements. We compare three
widely-adopted lag measuring methods: the Interpolated Cross-Correlation
Function (ICCF), the z-transformed Discrete Correlation Function (ZDCF) and the
MCMC code JAVELIN, for mock data with qualities typical of multi-object
spectroscopic reverberation mapping (MOS-RM) surveys that simultaneously
monitor hundreds of quasars. We quantify the overall lag detection efficiency,
the rate of false detections, and the quality of lag measurements for each of
these methods and under different survey designs (e.g., observing cadence and
depth) using mock quasar light curves. Overall JAVELIN and ICCF outperform ZDCF
in essentially all tests performed. Compared with ICCF, JAVELIN produces higher
quality lag measurements, is capable of measuring more lags with timescales
shorter than the observing cadence, is less susceptible to seasonal gaps and
S/N degradation in the light curves, and produces more accurate lag
uncertainties. We measure the Hbeta broad-line region size-luminosity (R-L)
relation with each method using the simulated light curves to assess the impact
of selection effects of the design of MOS-RM surveys. The slope of the R-L
relation measured by JAVELIN is the least biased among the three methods, and
is consistent across different survey designs. These results demonstrate a
clear preference for JAVELIN over the other two non-parametric methods for
MOS-RM programs, particularly in the regime of limited light curve quality as
expected from most MOS-RM programs.
