Reconciling the Quasar Microlensing Disc Size Problem with a Wind Model of Active Galactic Nucleus

TL;DR

This paper introduces a wind model that flattens the accretion disc temperature profile, reconciling observed quasar disc sizes from microlensing with theoretical expectations, and aligns size-mass relations with modified thin disc theory.

Contribution

It proposes a wind-driven disc model that explains the size discrepancy in quasar microlensing observations, incorporating angular momentum transfer for improved accuracy.

Findings

The wind model reduces the size discrepancy for several quasars.

Corrected disc sizes correlate with black hole mass as predicted by the modified model.

Inclusion of angular momentum transfer lowers the required wind strength.

Abstract

Many analyses have concluded that the accretion disc sizes measured from the microlensing variability of quasars are larger than the expectations from the standard thin disc theory by a factor of $\sim4$. We propose a simply model by invoking a strong wind from the disc to flatten its radial temperature profile, which can then reconcile the size discrepancy problem. This wind model has been successfully applied to several microlensed quasars with a wind strength $s\lesssim1.3$ by only considering the inward decreasing of the mass accretion rate (where $s$ is defined through $\dot{M}(R)\propto({R}/{R_{0}})^{s}$ ). After further incorporating the angular momentum transferred by the wind, our model can resolve the disc size problem with an even lower wind parameter. The corrected disc sizes under the wind model are correlated with black hole masses with a slope in agreement with our modified thin disc model.