Quantifying the impact of variable BLR diffuse continuum contributions
  on measured continuum inter-band delays
  We investigate the contribution of reprocessed continuum emission (1000A -
10,000A) originating in broad line region (BLR) gas, the diffuse continuum
(DC), to the wavelength-dependent continuum delays measured in AGN disk
reverberation mapping experiments. Assuming a spherical BLR geometry, we adopt
a Local Optimally-emitting Cloud (LOC) model for the BLR that approximately
reproduces the broad emission-line strengths of the strongest UV lines
(Ly-alpha and C IV) in NGC 5548. Within this LOC framework, we explore how
assumptions about the gas hydrogen density and column density distributions
influence flux and delay spectra of the DC. We find that: (i) models which
match well measured emission line luminosities and time delays also produce a
significant DC component, (ii) increased nH and/or NH, particularly at smaller
BLR radii, result in larger DC luminosities and reduced DC delays, (iii) in a
given continuum band the relative importance of the DC component to the
measured inter-band delays is proportional (though not 1:1) to its fractional
contribution to the total light in that band, (iv) the measured DC delays and
DC variability amplitude depends also on the variability amplitude and
characteristic variability timescale of the driving continuum, (v) the DC
radial surface emissivity distributions F(r) approximate power-laws in radius
with indices close to -2 (approximately 1:1 response to variations in the
driving continuum flux), thus their physics is relatively simple and less
sensitive to the unknown geometry and uncertainties in radiative transfer.
Finally, we provide a simple recipe for estimating the DC contribution in disk
reverberation mapping experiments.
