Double-peaked line profiles in AGNs-searching for reverberation from an accretion disk

If any part of the broad emission line in an AGN is coming from an accretion disk, it is theoretically possible that the line profile will vary in one day or less. In a particular application of the reverberation mapping technique (Stella 1990), variability of the line profile corresponding to a light crossing time of 5(r/1000r_g)M₈ days might be observed if the optical emission line region is ∼1,000 gravitational radii in size, as has been inferred for several double-peaked emitters (Chen & Halpern 1989; Eracleous & Halpern, this volume). If the disk is photoionized by a central, variable source, as is inferred from X-ray observations of several AGNs, then bumps in the optical line profiles will move from the wings to the core, as the wave of fluorescent emission proceeds from the inner, high velocity part of the disk to the outer, low velocity edge. Ideally, it is possible to make a direct measurement of the mass of the black hole with this technique. We report on a preliminary search for this effect in nightly spectroscopic monitoring of the Hα line profiles of half a dozen AGNs.