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We calculate the observable signature of a black hole accretion disk with agap or hole created by a secondary black hole embedded in the disk. We findthat for an interesting range of parameters of black hole masses (~10^6 to 10^9solar masses), orbital separation (~1 AU to ~0.1 pc), and gap width (10 to 190disk scale heights), the missing thermal emission from a gap manifests itselfin an observable decrement in the spectral energy distribution. We presentobservational diagnostics in terms of power-law forms that can be fit toline-free regions in AGN spectra or in fluxes from sequences of broad filters.Most interestingly, the change in slope in the broken power-law is almostentirely dependent on the width of gap in the accretion disk, which in turn isuniquely determined by mass ratio of the black holes, such that it scalesroughly as q^(5/12). Thus one can use spectral observations of the continuum ofbright active galactic nuclei to infer not only the presence of a closelyseparated black hole binary but also the mass ratio. When the black hole mergeropens an entire hole (or cavity) in the inner disk, the broad band SED of theAGN or quasar may serve as a diagnostic. Such sources should be especiallyluminous in optical bands but intrinsically faint in X-rays (i.e., not merelyobscured). We briefly note that viable candidates may have already beenidentified, though extant detailed modeling of those with high quality datahave not yet revealed an inner cavity.

Observable Consequences of Merger-Driven Gaps and Holes in Black Hole Accretion Disks