The Spatial Structure of An Accretion Disk

TL;DR

This study uses microlensing variability to measure the size and temperature structure of a quasar accretion disk, finding results consistent with thin disk models but with some deviations in slope and size.

Contribution

First measurement of quasar accretion disk size and structure using microlensing across multiple wavelengths, testing thin disk model predictions.

Findings

Measured B-band half-light radius of approximately 6.7 x 10^15 cm.

Found a temperature profile slope of about 0.61, close to the thin disk prediction of 0.75.

Results suggest a slightly shallower temperature slope and smaller disk size than standard models.

Abstract

Based on the microlensing variability of the two-image gravitational lens HE1104-1805 observed between 0.4 and 8 microns, we have measured the size and wavelength-dependent structure of the quasar accretion disk. Modeled as a power law in temperature, T proportional to R^-beta, we measure a B-band (0.13 microns in the rest frame) half-light radius of R_{1/2,B} = 6.7 (+6.2 -3.2) x 10^15 cm (68% CL) and a logarithmic slope of beta=0.61 (+0.21 -0.17) 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 x 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.