Quantifying the Diffuse Continuum Contribution of BLR Clouds to AGN Continuum Inter-band Delays

Understand

Disk reverberation mapping of a handful of nearby AGN suggest accretion disk sizes which are a factor few too large for their luminosities, apparently at odds with the standard model.

• Here, we investigate the likely contribution to the measured delay signature of diffuse continuum emission arising from broad line region gas.
• We start by constructing spherically symmetric pressure-law BLR models (i.e., $P(r)\propto r^{-s}$) that approximately reproduce the observed emission line fluxes of the strong UV--optical emission-lines in the best-studied source, NGC~5548.
• We then determine the contribution of the diffuse continuum to the measured continuum flux and inter-band delays, accounting for the observed variability behaviour of the ionizing nuclear continuum.