  X-ray Polarimetry is almost as old as X-ray Astronomy. Since the first
discovery of X-ray sources theoretical analysis suggested that a high degree of
linear polarization could be expected due either to the, extremely non thermal,
emission mechanism or to the transfer of radiation in highly asymmetric
systems. The actual implementation of this subtopic was, conversely, relatively
deceiving. This is mainly due to the limitation of the conventional techniques
based on the Bragg diffraction at 45deg, or on Thomson scattering around 90deg.
Acually no X-ray Polarimeter has been launched since 25 years. Nevertheless the
expectations from such measurement on several astrophysical targets including
High and Low Mass X-Ray Binaries, isolated neutron Stars, Galactic and
Extragalactic Black Holes is extremely attractive. We developed a new technique
to measure the linear polarization of X-ray sources. It is based on the
visualization of photoelectron tracks in a, finely subdivided, gas filled
detector (micropattern). The initial direction of the photoelectron is derived
and from the angular distribution of the tracks the amount and angle of
polarization is computed. This technique can find an optimal exploitation in
the focus of XEUS-1. Even in a very conservative configuration (basically the
already existing prototype) the photoelectric polarimeter could perform
polarimetry at % level on many AGNs. Further significant improvements can be
expected from a technological development on the detector and with the use of
XEUS-2 telescope.
