Re-examining the diffuse gamma-ray excess from the inner galaxy: Looking back at EGRET data in light of a modern Monte Carlo simulation

The Energetic Gamma Ray Experiment Telescope (EGRET) instrument onboard the Compton Gamma-ray Observatory (CGRO) has provided the most precise measurements of the gammaray sky to date. EGRET measurements of diffuse emission across the sky show an excess over commonly accepted models above 1 GeV. This "GeV excess" has been a topic of great debate and interest since its original discovery by Hunter et al. in 1997. This dissertation examines the ways in which GLAST simulation and reconstruction software have been modified to model EGRET. This detailed modeling has allowed exploration of the parameters of EGRET, in both its beam-test configuration and in-orbit on CGRO, in greater detail than has previously been published. The GeV excess is significantly increased when previously unaccounted for instrumental effects are considered. A re-scaled measurement of diffuse gamma-ray emission in the inner Galaxy is presented. A GALPROP model has been developed to reproduce the re-scaled observations.