The Optical, Ultraviolet, and X-ray Structure of the Quasar HE 0435-1223
  Microlensing has proven an effective probe of the structure of the innermost
regions of quasars, and an important test of accretion disk models. We present
light curves of the lensed quasar HE 0435-1223 in the R band and in the
ultraviolet, and consider them together with X-ray light curves in two energy
bands that are presented in a companion paper. Using a Bayesian Monte Carlo
method, we constrain the size of the accretion disk in the rest-frame near- and
far-UV, and constrain for the first time the size of the X-ray emission regions
in two X-ray energy bands. The R-band scale size of the accretion disk is about
10^15.23 cm (~23 r_g), slightly smaller than previous estimates, but larger
than would be predicted from the quasar flux. In the UV, the source size is
weakly constrained, with a strong prior dependence. The UV to R-band size ratio
is consistent with the thin disk model prediction, with large error bars. In
soft and hard X-rays, the source size is smaller than ~10^14.8 cm (~10 r_g) at
95% confidence. We do not find evidence of structure in the X-ray emission
region, as the most likely value for the ratio of the hard X-ray size to the
soft X-ray size is unity. Finally, we find that the most likely value for the
mean mass of stars in the lens galaxy is ~0.3 M_sun, consistent with other
studies.
