The accretion disc in the quasar SDSS J0924+0219

TL;DR

This study uses multi-wavelength observations of the lensed quasar SDSS J0924+0219 to analyze the size of its accretion disc, finding it inconsistent with the standard alpha-disc model.

Contribution

It provides the first direct size constraints on the quasar's accretion disc using microlensing and rules out the alpha-disc model with high confidence.

Findings

The anomalous flux ratio decreases with wavelength, indicating microlensing effects.

The continuum emission region's size is constrained to be less than 3.04E16 h70^{-1/2} (<M>/M_sun)^{1/2} cm.

The size-wavelength power-law index is constrained to be less than 1.34 at 95% confidence.

Abstract

We present single-epoch multi-wavelength optical-NIR observations of the "anomalous" lensed quasar SDSS J0924+0219, made using the Magellan 6.5-metre Baade telescope at Las Campanas Observatory, Chile. The data clearly resolve the anomalous bright image pair in the lensed system, and exhibit a strong decrease in the anomalous flux ratio with decreasing wavelength. This is interpreted as a result of microlensing of a source of decreasing size in the core of the lensed quasar. We model the radius of the continuum emission region, sigma, as a power-law in wavelength, sigma lambda^zeta. We place an upper limit on the Gaussian radius of the u'-band emission region of 3.04E16 h70^{-1/2} (<M>/M_sun)^{1/2} cm, and constrain the size-wavelength power-law index to zeta<1.34 at 95% confidence. These observations rule out an alpha-disc prescription for the accretion disc in SDSS J0924+0219 with 94% confidence.