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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 diskreverberation mapping experiments. Assuming a spherical BLR geometry, we adopta Local Optimally-emitting Cloud (LOC) model for the BLR that approximatelyreproduces the broad emission-line strengths of the strongest UV lines(Ly-alpha and C IV) in NGC 5548. Within this LOC framework, we explore howassumptions about the gas hydrogen density and column density distributionsinfluence flux and delay spectra of the DC. We find that: (i) models whichmatch well measured emission line luminosities and time delays also produce asignificant DC component, (ii) increased nH and/or NH, particularly at smallerBLR radii, result in larger DC luminosities and reduced DC delays, (iii) in agiven continuum band the relative importance of the DC component to themeasured inter-band delays is proportional (though not 1:1) to its fractionalcontribution to the total light in that band, (iv) the measured DC delays andDC variability amplitude depends also on the variability amplitude andcharacteristic variability timescale of the driving continuum, (v) the DCradial surface emissivity distributions F(r) approximate power-laws in radiuswith indices close to -2 (approximately 1:1 response to variations in thedriving continuum flux), thus their physics is relatively simple and lesssensitive to the unknown geometry and uncertainties in radiative transfer.Finally, we provide a simple recipe for estimating the DC contribution in diskreverberation mapping experiments.

Quantifying the impact of variable BLR diffuse continuum contributions on measured continuum inter-band delays