2008ApJ...673...34P

Based on the microlensing variability of the two-image gravitational lens HE 1104-1805 observed between 0.4 and 8 µm, we have measured the size and wavelength-dependent structure of the quasar accretion disk. Modeled as a power law in temperature, T∝R^–β, we measure a B-band (0.13 µm in the rest frame) half-light radius of R_1/2,B=6.7^+6.2_–3.2x10¹⁵ cm (68% confidence level) and a logarithmic slope of β=0.61^+0.21_–0.17 (68% confidence level) for our standard model with a logarithmic prior on the disk size. Both the scale and the slope are consistent with simple thin disk models where β=3/4 and R_1/2,B=5.9x10¹⁵ cm for a Shakura-Sunyaev disk radiating at the Eddington limit with 10% efficiency. The observed fluxes favor a slightly shallower slope, β=0.55^+0.03_–0.02, and a significantly smaller size for β=3/4.