The Average Size and Temperature Profile of Quasar Accretion Disks

Understand

We use multi-wavelength microlensing measurements of a sample of 10 image pairs from 8 lensed quasars to study the structure of their accretion disks.

• By using spectroscopy or narrow band photometry we have been able to remove contamination from the weakly microlensed broad emission lines, extinction and any uncertainties in the large-scale macro magnification of the lens model.
• We determine a maximum likelihood estimate for the exponent of the size versus wavelength scaling ($r_s\propto \lambda^p$ corresponding to a disk temperature profile of $T\propto r^{-1/p}$) of $p=0.75^{+0.2}_{-0.2}$, and a Bayesian estimate of $p=0.8\pm0.2$, which are significantly smaller than the prediction of thin disk theory ($p=4/3$).
• We have also obtained a maximum likelihood estimate for the average quasar accretion disk size of $r_s=4.5^{+1.5}_{-1.2} $ lt-day at a rest frame wavelength of $\lambda = 1026~{\mathrm \AA}$ for microlenses with a mean mass of $M=1 M_\sun$, in agreement with previous results, and larger than expected from thin disk theory.