The panels show snapshots from the X-Calibur event analysis for ~16 hours of data taken in Palestine. The top image shows which pixels fired, projecting the four sides of the X-Calibur polarimeter into a plane. The lower two 32-pixel islands are from the “17th detector” which is located below the polarimeter and will image of the X-ray source so that the pointing of the telescope can be verified based on in-flight X-ray data. On the ground, the signals are produced by cosmic rays striking the detector. In flight, we will look at photons from neutron stars and black holes in orbit with stellar companions gobbling up the matter from the companion stars. The bottom image shows the energy spectrum of the measured cosmic ray events with a small peak at the high-energy end of the dynamic range where the readout saturates. The photons from cosmic objects are expected to show up in the energy range from 20-60 keV (X-rays with 10,000-30,000 times the energy of visible photons from the Sun). The detector performance (in terms of energy threshold and energy resolution) fully meets the requirements and surpasses the expectations after engineers Paul Dowkontt and Gianluigi de Geronimo, research professor Fabian Kislat, electrical technician Garry Simburger, and graduate students Banafsheh Beheshtipour and Quin Abarr worked on optimizing the detector for more than a year.