  A tendency for the axes of double-lobed radio quasars to be aligned with the
electric vectors of optical polarization in the active galactic nuclei is
well-known. However, the origin of the polarization and reason behind its
correlation with radio morphology is not yet established. From accurate
spectropolarimetry of 7 quasars which show this alignment effect, we find that
the polarization is universally confined to the continuum, and not shared by
the line emission or 3000A bump. Over the observed region 4000-8000A, the
spectral indices of polarized flux, P x Flambda, are consistent with uniform
polarization applied to the light of the big blue bump or with synchrotron
emission. However, electron scattering from an optically-thick, geometrically-
thin, accretion disk is well-known to give rise to a polarization position
angle that is perpendicular to the disk axis. Optical synchrotron emission akin
to that shown to exist in the miniblazar 3C273 is a more attractive
explanation, and supporting evidence can be found for some of the targets in
the form of polarimetric variability over intervals of years. Properties of the
most strongly-polarized radio-optical aligned quasars can be explained by
misdirected blazar core components that have net polarizations of P~10% and
provide ~10% of the total optical light.

Astrophysics