Design and Performance of the Next-Generation Hard X-Ray Polarimeter XL-Calibur

XL-Calibur is a balloon-borne hard X-ray (15-80 keV) polarimetry mission. This mission is the successor to X-Calibur, which observed the accreting neutron star GX 301-2 from Antarctica during the 2018-19 austral summer. The 12-meter-long XL-Calibur truss accommodates the mounting of an X-ray mirror on one end that focuses X-rays onto the polarimeter affixed on the opposite end. The polarimeter comprises a Beryllium scattering rod surrounded by Cadmium Zinc Telluride (CZT) detectors with an energy resolution of ~3.5 keV. Pointing with arcsecond accuracy is facilitated by the Wallops Arc Second Pointer system. XL-Calibur will see a considerable sensitivity improvement over X-Calibur by using a larger effective area X-ray mirror along with a factor of 25 lower background count rate through the combined use of thinner CZT detectors and improved anticoincidence shielding. This talk will describe the design, performance, and science goals of the XL-Calibur mission.