Simulation of Black Hole Inner Accretion Disk-Corona and Optimization of the Hard X-ray Polarimeter, X-Calibur

Mass accreting stellar mass and supermassive black holes are strong sources of X-rays. The X- ray observations enable studies of the process of black hole accretion and give us information about the spacetime background. In the framework of my thesis work, I have continued the development of a general-relativistic ray-tracing code enabling the simulation of the Comptonization of photons in the hot accretion disk corona. I use the code to investigate the impact of various approximation schemes for modeling the Comptonization finding that a fully relativistic treatment is needed for accurate predictions in the soft and hard X- ray regimes (0.1-100 keV). I use the code to study the impact of the 3-D geometry of the corona on the observed X-ray flux and polarization energy spectra. Furthermore, I study the observational signatures of accretion disk hotspots orbiting the black holes. Such orbiting hotspots have been invoked to explain the presence of high-frequency quasi-periodic oscillations (HFQPOs) in the X-ray light curves from several accreting stellar-mass black holes. I use the newly developed numerical tools to model the properties of one supermassive black hole (Mrk 335) and one stellar mass black hole (GRS 1915+105). I conclude with a discussion of the scientific potential of spectral, timing, and polarimetric studies of black holes with missions such as the Imaging X-ray Polarimetry Explorer (IXPE) and the enhanced X-ray Timing and Polarimetry Mission (eXTP). As a graduate student, I played an active role in preparing the X-Calibur hard X-ray polarization mission for a long duration balloon flight from McMurdo in December 2018. My work aimed at reducing the readout noise of the polarimeter's Cadmium Zinc Telluride (CZT) detectors. My work contributed to a substantially lower energy threshold and thus a substantially improved sensitivity of X- Calibur.