A Fresh Look at Diffuse Gamma-ray Emission from the Inner Galaxy

TL;DR

This paper revisits the diffuse gamma-ray emission from the inner Galaxy, revealing that instrumental effects significantly influence the observed GeV excess in EGRET data.

Contribution

It introduces a detailed simulation of the EGRET instrument, showing that the GeV excess is amplified when accounting for previously neglected instrumental effects.

Findings

The GeV excess is more pronounced after considering instrumental effects.

Detailed modeling of EGRET improves understanding of gamma-ray measurements.

Revised measurements of diffuse gamma-ray emission in the inner Galaxy are presented.

Abstract

The Energetic Gamma-Ray Experiment Telescope (EGRET) experiment onboard the Compton Gamma-Ray Observatory (CGRO) has provided the most precise measurements of the gamma-ray sky to date. The EGRET measurements of the diffuse emission across the sky show an excess 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. We have modified the GLAST simulation and reconstruction software to model the EGRET instrument. This detailed modeling has allowed us to explore the parameters of the EGRET instrument, in both its beam-test configuration and in-orbit on CGRO, in greater detail than has previously been published. We have found that the GeV excess is significantly increased when previously unaccounted for instrumental effects are considered. We will present a new measurement of diffuse gamma-ray emission in the inner Galaxy.