HX-POL - A Balloon-Borne Hard X-Ray Polarimeter

TL;DR

HX-POL is a balloon-borne hard X-ray polarimeter designed to measure polarization of cosmic X-ray sources between 50 keV and 400 keV, enabling insights into particle acceleration near compact objects.

Contribution

This paper introduces the design and estimated performance of HX-POL, a novel balloon-borne instrument utilizing Si and CZT detectors for X-ray polarization measurements.

Findings

Laboratory tests validate detector performance.

HX-POL can measure polarization below 10% in one-day flights.

Longer flights can detect polarization degrees of a few percent.

Abstract

We report on the design and estimated performance of a balloon-borne hard X-ray polarimeter called HX-POL. The experiment uses a combination of Si and Cadmium Zinc Telluride detectors to measure the polarization of 50 keV-400 keV X-rays from cosmic sources through the dependence of the angular distribution of Compton scattered photons on the polarization direction. On a one-day balloon flight, HX-POL would allow us to measure the polarization of bright Crab-like sources for polarization degrees well below 10%. On a longer (15-30 day) flight from Australia or Antarctica, HX-POL would be be able to measure the polarization of bright galactic X-ray sources down to polarization degrees of a few percent. Hard X-ray polarization measurements provide unique venues for the study of particle acceleration processes by compact objects and relativistic outflows. In this paper, we discuss the overall instrument design and performance. Furthermore, we present results from laboratory tests of the Si and CZT detectors.