Limits of Applicability of the Geometrical Optics in Analyzing Observations of Gravitationally Lensed Quasars

Abstract

Propagation of quasar radiation through a galaxy is analyzed, accounting
for gravitational focusing of the light rays by compact
masses distributed inside the galaxy volume. It is shown that the
absence of total correlation between fluctuations of the macroimage
brightness in different wavelengths observed in microlensing
can be explained not only by the wavelength dependence of
a quasar dimension but also by properties of the galaxy medium
where the quasar radiation is propagating. To distinguish between
the effects of the galaxy medium and parameters of the source
quasar, the dedicated quasi-synchronous observations of a gravitationally
lensed quasar at two telescopes of different diameters
should be carried out. Such observations in different spectral ranges
will provide the estimation of statistical properties of the
galaxy medium, which are determined by the density and distribution
of masses in the lensing galaxy, as well as determination of the
wavelength dependence of the quasar size.