Gravitational Lensing Signatures of Supermassive Black Holes in Future   Radio Surveys
  Observational measurements of the relationship between supermassive black holes (SMBHs) and the properties of their host galaxies are an important method for probing theoretical hierarchical growth models. Gravitational lensing is a unique mechanism for acquiring this information in systems at cosmologically significant redshifts. We review the calculations required to include SMBHs in two standard galactic lens models, a cored isothermal sphere and a broken power law. The presence of the SMBH produces two primary effects depending on the lens configuration, either blocking the ``core'' image that is usually predicted to form from a softened lens model, or adding an extra, highly demagnified, image to the predictions of the unaltered lens model. The magnitudes of these effects are very sensitive to galaxy core sizes and SMBH masses. Therefore, observations of these lenses would probe the properties of the inner regions of galaxies, including their SMBHs. Lensing cross-sections and optical depth calculations indicate that in order to fully observe these characteristic signatures, flux ratios of order 10^6 or more between the brightest and faintest images of the lens must be detectable, and thus the next generation of radio telescope technology offers the first opportunity for a serious observational campaign. Core images, however, are already detectable and with additional observations their statistics may be used to guide future SMBH searches. 
Judd D. Bowman, Jacqueline N. Hewitt, James R. Kiger