Based on the microlensing variability of the two-image gravitational lens HEÂ 1104–1805 observed between 0.4 and 8 ~ { } \mu m , we have measured the size and wavelength-dependent structure of the quasar accretion disk .
Modeled as a power law in temperature , T \propto R ^ { - \beta } , we measure a B-band ( 0.13 ~ { } \mu m in the rest frame ) half-light radius of R _ { 1 / 2 , B } = 6.7 ^ { +6.2 } _ { -3.2 } \times 10 ^ { 15 } ~ { } cm ( 68 \% CL ) and a logarithmic slope of \beta = 0.61 ^ { +0.21 } _ { -0.17 } ( 68 \% CL ) 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 \beta = 3 / 4 and R _ { 1 / 2 , B } = 5.9 \times 10 ^ { 15 } ~ { } cm for a Shakura-Sunyaev disk radiating at the Eddington limit with 10 \% efficiency .
The observed fluxes favor a slightly shallower slope , \beta = 0.55 ^ { +0.03 } _ { -0.02 } , and a significantly smaller size for \beta = 3 / 4 .