Microlensing Evidence for Super-Eddington Disc Accretion in Quasars

TL;DR

Microlensing observations suggest some quasars are undergoing super-Eddington accretion, forming optically-thick envelopes that enlarge apparent disc sizes and are wavelength-independent, challenging standard accretion models.

Contribution

This paper introduces a model linking microlensing data to super-Eddington accretion, explaining larger-than-expected disc sizes in quasars.

Findings

Evidence for super-Eddington accretion in some quasars.

Super-Eddington accretion causes optically-thick envelopes that enlarge apparent disc sizes.

The model allows estimating black hole masses and accretion rates from microlensing data.

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.