Exploring the Hard X-ray Polarization of Southern Hemisphere X-Ray Sources with a Long-Duration Balloon Flight of X-Calibur

X-Calibur is a balloon borne hard X-ray polarimetry mission combining a grazing incidence 8m focal length X-ray mirror with a hard X-ray scattering polarimeter made of a scattering element surrounded by an assembly of Cadmium Zinc Telluride (CZT) detectors. The combination of a focusing multilayer mirror with and an actively shielded polarimeter gives X-Calibur excellent sensitivity and energy resolutions over the broad energy range from 20 keV to 60 keV. After a conventional 1-day test flight from Fort Sumner, we apply here for supplementary funding for a December 2018-January 2019 Long Duration Balloon (LDB) flight. The LDB flight will be launched from McMurdo (Antarctica) and will will allow us to measure the 20-60 keV X-ray polarization properties of flaring X-ray binaries, the supergiant X-ray binaries Vela X-1, GX 301-2, and 4U 1700-377, and the prototypical radio galaxy Centaurus A. The LDB flight will take advantage of an optimized polarimeter and shielding design which improves the overall signal-to-noise ratio by a factor of three compared to the original design. More »