Polarimetry with a soft x-ray spectrometer

TL;DR

This paper presents a novel method for measuring linear X-ray polarization across a broad energy band using multilayer-coated optics and spectroscopic techniques, enabling high modulation factors for space-based observations.

Contribution

It introduces a new spectrometer design that combines multilayer optics and gratings to measure X-ray polarization with high efficiency over 0.2 to 0.8 keV.

Findings

Achieves modulation factors over 80% across the band

Uses multilayer-coated flats for broad-band spectropolarimetry

Suitable for small orbiting X-ray missions

Abstract

An approach for measuring linear X-ray polarization over a broad-band using conventional spectroscopic optics is described. A set of multilayer-coated flats reflect the dispersed X-rays to the instrument detectors. The intensity variation as a function of energy and position angle is measured to determine three Stokes parameters: I, Q, and U. By laterally grading the multilayer optics and matching the dispersion of the gratings, one may take advantage of high multilayer reflectivities and achieve modulation factors over 80% over the entire 0.2 to 0.8 keV band. A sample design is shown that could be used with a small orbiting mission.