Balloon-borne hard X-ray polarimetry with PoGOLite

TL;DR

PoGOLite is a balloon-borne X-ray polarimeter designed to measure polarization in the 25-100 keV range from astrophysical sources, utilizing Compton scattering in a stabilized stratospheric platform.

Contribution

This paper introduces the design, implementation, and initial flight results of PoGOLite, a novel balloon-borne instrument for X-ray polarimetry of compact sources.

Findings

First balloon flight of PoGOLite was conducted.

Instrument successfully measured X-ray polarization from targets.

The maiden flight provided valuable data despite being ill-fated.

Abstract

PoGOLite is a hard X-ray polarimeter operating in the 25-100 keV energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-X1. The polarisation of incoming photons is determined using coincident Compton scattering and photo-absorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.