Burnett, ThompsonRoth, Marshall2012-09-132013-03-132012-09-132012Roth_washington_0250E_10446.pdfhttp://hdl.handle.net/1773/20699Thesis (Ph.D.)--University of Washington, 2012The Large-Area Telescope (LAT) on the <italic>Fermi</italic> Gamma-Ray Space Telescope is a pair-conversion gamma-ray telescope with unprecedented capability to image astrophysical gamma-ray sources between 20 MeV and 300 GeV. The pre-launch performance of the LAT, decomposed into effective area, energy and angular dispersions, were determined through extensive Monte Carlo (MC) simulations and beam tests. The point-spread function (PSF) characterizes the angular distribution of reconstructed photons as a function of energy and geometry in the detector. Here we present a set of likelihood analyses of LAT data based on the spatial and spectral properties of sources, including a determination of the PSF on orbit. We find that the PSF on orbit is generally broader than the MC at energies above 3 GeV and consider several systematic effects to explain this difference. We also investigated several possible spatial models for pair-halo emission around BL Lac AGN and found no evidence for a component with spatial extension larger than the PSF.application/pdfen-USCopyright is held by the individual authors.agn; Fermi; gamma-ray; LAT; tevAstrophysicsPhysicsThesis