Spectroscopy and polarimetry of the gravitationally lensed quasar
  Q0957+561
  We present new spectroscopic and polarimetric observations of the first
discovered gravitational lens Q0957+561 obtained with the 6m telescope of the
Special Astrophysical Observatory (SAO, Russia). We explore spectropolarimetric
parameters of Q0957+561 A,B components to investigate the innermost structure
of the quasar, and explore the nature of polarization in lensed quasars.
Additionally, we compare their present-day spectral characteristics with
previous observations in order to study long-term spectral changes. We analyze
spectral characteristics of lensed quasar comparing spectra of A and B images,
as well as comparing previously observed image spectra with present-day ones.
The polarization parameters of A-B images are compared. We also model the
macro-lens influence on the polarization of the images representing the
gravitational lens with a singular isothermal elliptical potential.
  We find that the brightness and SED ratio of components A and B changed
during a long period. Polarization in broad lines of components A and B showed
that the equatorial scattering cannot be detected in this quasar. We find
wavelength-dependent polarization that may be explained as a combination of the
polarization from the disc and outflowing material. There is a significant
difference between polarization parameters of the A and B images: the B
component shows a higher polarization degree and polarization angle. However,
both polarization vectors are nearly perpendicular to the observed radio jet
projection. It indicates that the polarization in the continuum is coming from
the accretion disc. Our simple lensing model of a polarized source showed that
macro-lens can cause the observed differences in polarization parameters of
Q0957+561 A,B images. Using Mg II broad line and luminosity of component A we
estimated that the Q0957+561 black hole mass is M~(4.8-6.1) $10^8$ M$\odot$
