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Some Type-1 active galactic nuclei (AGNs) are showing extremely asymmetricBalmer lines with the broad peak redshifted or blueshifted by thousands ofkm/s. These AGNs may be good candidates for supermassive binary black holes(SMBBHs). The complex line shapes can be very well due to the complexkinematics of the two broad line regions (BLRs). Therefore another methodsshould be applied to confirm the SMBBHs. One of them is spectropolarimetry. Werely on numerical modeling of the polarimetry of binary black holes systemssince polarimetry is sensitive to geometry, in order to find specific influenceof supermassive binary black hole (SMBBH) geometry and dynamics on polarizedparameters across the broad line profiles. We apply our method to SMBBHs inwhich both components are assumed to be AGNs with distances at the sub-pcscale. We use a Monte Carlo radiative transfer code that simulates thegeometry, dynamics and emission of a binary system where two black holes aregetting increasingly closer. Each gravitational well is accompanied by its ownBLR and the whole system is surrounded by an accretion flow from the distanttorus. We examine the emission line deformation and predict the polarizationthat could be observed. We model broad line polarization for various BLRgeometries with complex kinematics. We find that the presence of SMBBHs canproduce complex polarization angle profiles and strongly affect the polarizedand unpolarized line profiles. Depending on the phase of the SMBBH, theresulting double-peaked emission lines either show red or blue peak dominance,or both the peak can have the same intensity. In some cases, the whole lineprofile appears as a single Gaussian line, hiding the true nature of thesource. Our results suggest that observations with the high resolutionspectropolarimetry of optical broad emission lines could play an important rolein detecting sub-pc SMBBHs.

Predicting the broad lines polarization emitted by supermassive binary black holes