Microlensing Evidence for Super-Eddington Disc Accretion in Quasars

Abstract

Microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disc structure in strongly lensed quasars. Disc sizes estimated this way are on average larger than the predictions of the standard Shakura-Sunyaev accretion disk model. Analysing the observational data on microlensing variability allows to suggest that some fraction of lensed quasars (primarily, smaller-mass objects) are accreting in super-Eddington regime. Super-Eddington accretion leads to formation of an optically-thick envelope scattering the radiation formed in the disc. This makes the apparent disc size larger and practically independent of wavelength. In the framework of our model, it is possible to make self-consistent estimates of mass accretion rates and black hole masses for the cases when both amplification-corrected fluxes and radii are available.