HX-POL - a balloon-borne hard X-ray polarimeter

We report on the conceptual 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-500 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 strong Crab-like sources for polarization degrees down to 5%. On a longer (15–30 day) flight from Australia or Antarctica, HX-POL would be be able to measure the polarization of strong sources down to polarization degrees of 1%. Hard X-ray polarization measurements provide unique venues for the study of particle acceleration processes by compact objects. In this contribution, we discuss the overall instrument design and performance. Furthermore, we present results from laboratory tests of the Si and CZT detectors.