POLARIZING PROPERTIES OF GRAZING-INCIDENCE X-RAY MIRRORS - COMMENT

We show that grazing-incidence telescopes, like those used for x-ray i maging, present negligible instrumental polarization. This property do es not depend on the number of reflections the telescope employs to le ad light from the entrance pupil to the focal plane. The result applie s to the various mirrors of the advanced x-ray astrophysics facility s atellite. In this particular case we have quantified the residual inst rumental polarization to be between 10(-3) and 5 x 10(-5), depending o n the size of the resolution elements.