We present a microlensing analysis of 61 Chandra observations of 14 quadruply lensed quasars. X-ray flux measurements of the individual quasar images give a clean determination of the microlensing effects in the lensing galaxy and thus offer a direct
assessment of the local fraction of stellar matter making up the total integrated mass along the lines of sight through the lensing galaxy. A Bayesian analysis of the ensemble of lensing galaxies gives a most likely local stellar fraction of 7%, with the other 93% in a smooth, dark matter component, at an average impact parameter R_c of 6.6 kpc from the center of the lensing galaxy. We divide the systems into smaller ensembles based on R_c and find that the most likely local stellar fraction varies qualitatively and quantitatively as expected, decreasing as a function of R_c.
We determine the most likely dark-matter fraction in the elliptical galaxy quadruply lensing the quasar PG1115+080 based on analyses of the X-ray fluxes of the individual images in 2000 and 2008. Between the two epochs, the A2 image of PG1115+080 bri
ghtened relative to the other images by a factor of six in X-rays. We argue that the A2 image had been highly demagnified in 2000 by stellar microlensing in the intervening galaxy and has recently crossed a caustic, thereby creating a new pair of micro-images and brightening in the process. Over the same period, the A2 image has brightened by a factor of only 1.2 in the optical. The most likely ratio of smooth material (dark matter) to clumpy material (stars) in the lensing galaxy to explain the observations is ~90% of the matter in a smooth dark-matter component and ~10% in stars.
