The accretion disc in the quasar SDSS J0924+0219

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, σ, as a power-law in wavelength, σ ∝ λ . We place an upper limit on the Gaussian radius of the u′-band emission region of 3.04×1016h 70 (〈M〉/M ) cm, and constrain the size-wavelength power-law index to ζ < 1.34 at 95% confidence. These observations rule out an alpha-disc prescription for the accretion disc in SDSS J0924+0219 with 94% confidence.