  We study linear polarization due to scattering of light on a cloudlet of
particles, taking into account the radiation drag and the gravitational pull
exerted on them by a central body. Effects of special and general relativity
are included by connecting a model of Beloborodov (1998) for the local
polarization of scattered light with Abramowicz, Ellis & Lanza (1990) formalism
for the particle motion near an ultra-compact star. Compactness of the central
body and its luminosity are two critical parameters of the model. We discuss
the polarization magnitude of photons, which are Thomson-scattered into direct
and higher-order images. Importance of the latter is only moderate under
typical conditions, but they may give rise to distinct features, which we
explore in terms of a toy model. The scattered signal exhibits variations of
intensity and of polarization with mutual time-lags depending on the
beaming/focusing effects and the light travel time.
