A Transmissive X-ray Polarimeter Design For Hard X-ray Focusing Telescopes

TL;DR

This paper proposes a novel transmissive X-ray polarimeter design for hard X-ray telescopes, enhancing detection efficiency and science return while maintaining low cost and sensitivity, supported by preliminary lab tests.

Contribution

It introduces a new gas chamber-based polarimeter with a transmissive design that improves efficiency for hard X-ray telescopes.

Findings

Achieves nearly 80% transmission at 6 keV

Expected minimum detectable polarization of 3% for a 1mCrab source

Preliminary lab tests show promising photoelectron tracks and modulation curves

Abstract

The X-ray Timing and Polarization (XTP) is a mission concept for a future space borne X-ray observatory and is currently selected for early phase study. We present a new design of X-ray polarimeter based on the time projection gas chamber. The polarimeter, placed above the focal plane, has an additional rear window that allows hard X-rays to penetrate (a transmission of nearly 80% at 6 keV) through it and reach the detector on the focal plane. Such a design is to compensate the low detection efficiency of gas detectors, at a low cost of sensitivity, and can maximize the science return of multilayer hard X-ray telescopes without the risk of moving focal plane instruments. The sensitivity in terms of minimum detectable polarization, based on current instrument configuration, is expected to be 3% for a 1mCrab source given an observing time of 10^5 s. We present preliminary test results, including photoelectron tracks and modulation curves, using a test chamber and polarized X-ray sources in the lab.