The Steady-State Multi-TeV Diffuse Gamma-Ray Emission Predicted with GALPROP and Prospects for the Cherenkov Telescope Array

Abstract

Cosmic Rays (CRs) interact with the diffuse gas, radiation, and magnetic fields in the interstellar medium (ISM) to produce electromagnetic emissions that are a significant component of the all-sky flux across a broad wavelength range. The Fermi Large Area Telescope (LAT) has measured these emissions at GeV $\gamma$-ray energies with high statistics. Meanwhile, the High-Energy Stereoscopic System (H.E.S.S.) telescope array has observed large-scale Galactic diffuse emission in the TeV $\gamma$-ray energy range. The emissions observed at GeV and TeV energies are connected by the common origin of the CR particles injected by the sources, but the energy dependence of the mixture from the general ISM (true `diffuse'), those emanating from the relatively nearby interstellar space about the sources, and the sources themselves, is not well understood. In this paper, we investigate predictions of the broadband emissions using the GALPROP code over a grid of steady-state 3D models that include variations over CR sources, and other ISM target distributions. We compare, in particular, the model predictions in the VHE ($\ge$100 GeV) $\gamma$-ray range with the H.E.S.S. Galactic plane survey (HGPS) after carefully subtracting emission from catalogued $\gamma$-ray sources. Accounting for the unresolved source contribution, and the systematic uncertainty of the HGPS, we find that the GALPROP model predictions agree with lower estimates for the HGPS source-subtracted diffuse flux. We discuss the implications of the modelling results for interpretation of data from the next generation Cherenkov Telescope Array (CTA).

14 pages, 12 figures, Accepted in MNRAS

References in corpus (18)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Observations of the Crab Nebula with H.E.S.S
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons
• Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth
• Radio observational constraints on Galactic 3D-emission models
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• First Detection of sub-PeV Diffuse Gamma Rays from the Galactic Disk: Evidence for Ubiquitous Galactic Cosmic Rays beyond PeV Energies
• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) I: Project Overview and Initial Results
• Gamma rays from molecular clouds
• High-Energy Gamma Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium
• A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
• Cosmic-Ray Propagation in Light of Recent Observation of Geminga
• The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and HI overview
• The Mopra Southern Galactic Plane CO Survey - Data Release 3
• The Mopra Southern Galactic Plane CO Survey - Data Release 1
• A New Multi-Tracer Approach to Defining the Spiral arm width in the Milky Way