Super-Eddington accretion in the Q2237+0305 quasar?

TL;DR

This study investigates the interband time lags in the Q2237+0305 quasar and suggests that super-Eddington accretion with an extended scattering envelope explains the observed larger-than-expected time delays, challenging standard accretion disk models.

Contribution

The paper provides observational evidence for super-Eddington accretion in a quasar by linking interband time lags to an extended scattering envelope around the accretion disk.

Findings

Interband time lags exceed standard model predictions.

Super-Eddington accretion envelope parameters match observed lags.

Extended scattering envelope explains increased apparent disk size.

Abstract

The interband time lags between the flux variations of the Q2237+0305 quasar have been determined from light curves in the Johnson-Cousins V, R, and I spectral bands. The values of the time lags for filter pairs R-V, I-R, and I-V are significantly higher than those predicted by the standard accretion disk model by Shakura and Sunyaev. To explain the discrepancy, the idea of a supercritical accretion regime in quasars considered in 1973 by Shakura and Sunyaev is applied. This regime has been shown by them to cause an extended scattering envelope around the accretion disk. The envelope efficiently scatters and re-emits the radiation from the accretion disk and thus increases the apparent disk size. We made use of analytical expressions for the envelope radius and temperature derived by Shakura and Sunyaev in their analysis of super-Eddington accretion and show that our results are consistent with the existence of such an envelope. The corresponding parameters of the accretion regime were calculated. They provide the radii of the envelope in the V, R, and I spectral bands consistent with the inter-band time lags determined in our work.