The Use of Laterally Graded Multilayer Mirrors for Soft X-ray Polarimetry

TL;DR

This paper discusses the development of laterally graded multilayer mirrors for soft X-ray polarimetry, enabling broad spectral polarization measurements with high modulation factors and potential applications in astrophysical observations.

Contribution

It introduces a new phase of LGML development that allows polarization of X-rays from various sources and outlines plans for a suborbital rocket experiment for astrophysical polarization detection.

Findings

Achieved over 50% modulation factor across 0.2-0.8 keV band.

Demonstrated 100% polarized X-rays at 0.525 keV.

Developed a system for testing polarimeter components from 0.15-0.70 keV.

Abstract

We present continued development of laterally graded multilayer mirrors (LGMLs) for a telescope design capable of measuring linear X-ray polarization over a broad spectral band. The multilayer-coated mirrors are used as Bragg reflectors at the Brewster angle. By matching to the dispersion of a spectrometer, one may take advantage of high multilayer reflectivities and achieve modulation factors over 50% over the entire 0.2-0.8 keV band. In Phase II of the polarimetry beam-line development, we demonstrated that the system provides 100% polarized X-rays at 0.525 keV (Marshall et al. 2013). Here, we present results from phase III of our development, where a LGML is used at the source and laterally manipulated in order to select and polarize X-rays from emission lines for a variety of source anodes. The beamline will then provide the capability to test polarimeter components across the 0.15-0.70 keV band. We also present plans for a suborbital rocket experiment designed to detect a polarization level of better than 10% for an active galactic nucleus.