The effect of a variable anisotropic continuum source upon the broad emission line profiles and responses

The large diversity observed among broad emission line profiles in active galactic nuclei (AGNs) is here examined in the context of a simple unifying scheme. We propose a model for the broad-line region (BLR) consisting of a spherical distribution of optically thick clouds moving along randomly inclined circular Keplerian orbits and illuminated by a strong, central, variable anisotropic continuum source. This simple model is capable of reproducing a large fraction of the observed range in broad emission line profiles, including both single- and double-peaked profiles and profiles with prominent shoulders. A strong prediction of this model is that double-peaked profiles will in general show larger equivalent widths and larger full widths at half-maximum than single-peaked profiles.