(Georgia Institute of Technology, 2022-05)
Xiang, Xin
Warm coronae, Comptonizing regions of warm (temperature kT ∼ 1keV), and optically thick (Thomson depth ∼ 10 - 20) gas, at the surfaces of accretion disks in active galactic nuclei (AGNs), have been proposed to explain the origin of the soft X-ray excess commonly observed in the X-ray spectra of AGNs. We calculate the X-ray emission from an irradiated constant density accretion disk atmosphere that includes heating from a warm corona, as well as illumination from an external X-ray power-law radiation, and blackbody emission from the dissipation in the accretion disk. The model accounts for the radial dependence of disk ionization, including the effects of light-bending on the illuminating X-rays. The final spectra are produced by integrating the local reflection/emission spectrum from approximately 2 to 400 gravitational radii. We demonstrate how the soft excess in AGN X-ray spectra depends on the warm corona parameters, including the heating fraction and optical depth, and the strength of the X-ray illumination. The model will be publicly released in 2022 for use in fitting AGN spectra.
(Georgia Institute of Technology, 2015-08-18)
Berger, Eric M.
The goal of this study is to explore the mechanism by which unstable toroidal droplets collapse inwardly. As such, particle image velocimetry methods will be employed in obtaining an experimental picture of the velocity field inside of unstable toroidal droplets as they collapse. The inward collapse exhibited by unstable toroidal droplets is unique to the geometry of the torus and is therefore physically interesting. There is currently not an available experimental picture of this collapse, so this study will attempt to fill that void. Ultimately the results of this study will be compared against the currently accessible theoretical pictures of collapsing toroidal droplets, leading to further refinements in the field.