Ray-tracing a small orbital mission for soft-X-ray polarimetry

TL;DR

This paper proposes a small, cost-effective orbital mission concept utilizing advanced multilayer mirrors for X-ray polarimetry below 2 keV, filling a gap in current observational capabilities and demonstrating its feasibility through ray-tracing simulations.

Contribution

It introduces a novel small satellite mission design using multilayer mirror technology for X-ray polarimetry below 2 keV, with detailed ray-tracing analysis and scalability considerations.

Findings

Ray-tracing results validate the mission concept.

Design parameters for the optical components are established.

Scalability to multiple channels is feasible.

Abstract

X-ray polarimetry is still largely uncharted territory. With the upcoming launch of IXPE, we will learn a lot more about X-ray polarization at energies above 2 keV, but so far no current or accepted mission provides observational capabilities below 2 keV. We present ray-tracing results for a small orbital mission that could be launched within NASA's Pioneer or SmallSat cost-cap to provide X-ray polarimetry below 2 keV. The design is based on the use of laterally-graded multi-layer (ML) mirrors, a concept that we have developed theoretically for the REDSoX Polarimeter, for which most components have been verified in the laboratory. In this contribution, we describe a single channel orbital mission based on the same idea, but modified to the unique cost and space requirements. All results scale up easily to two or more polarimetry channels. Scaling up would simply increase the effective area and reduce the need to rotate the instrument to measure the different polarization directions. In particular, we use the ray-traces to define the maximum size of the dispersion gratings and to determine an alignment budget.