Multilayer mirror-based soft X-ray polarimeter for astronomical observations

A simple design of a soft X-ray polarimeter using multilayer mirrors is presented. A multilayer mirror acts as a linear polarization analyzer for X-rays at incidence angles close to the Brewster angle. The instrument consists of an X-ray concentrator, a set of multilayer mirrors placed at 45 deg from the optical axis, and a detector at Nasmyth focus. The instrument rotating about its optical axis during observations can measure the linear polarization of 0.2-to 0.7-keV X-rays from astronomical sources. The use of a soft X-ray concentrator with geometrical area ∼630 cm² provides sufficient sensitivity to address key scientific questions. Five different multilayer mirrors placed on a rotating wheel provide the option to measure polarization in any of the five narrow bands spanning the 0.2-to 0.7-keV range. Design and estimated performance of the design are discussed.