First Results from the X-Calibur Hard X-Ray Polarimetry Experiment
Hard X-ray polarimetric observations of neutron stars, magnetars, and mass accreting black holes can give us qualitatively new information about the geometry and properties of the X-ray emission regions, and can test fundamental physics laws in regimes that cannot be probed in terrestrial laboratories. In this talk, I will present first results from the X-Calibur experiment, a Washington University led hard X-ray polarimetry mission. The experiment was flown end of December 2018 for a short two-day high-altitude balloon flight from McMurdo Antarctica). I will report here on the X-Calibur observations of the accreting pulsar GX 301-2, giving us the first observational constraints on the linear polarization properties of the emission in a particularly interesting energy band where plasma and vacuum birefringence strongly impact the net polarization. I will close with describing our plans for longer follow-up flights with an improved science payload in 2021, 2022 and 2024.