Deciphering Residual Emissions: Time-Dependent Models for the Non-Thermal Interstellar Radiation from the Milky Way

Abstract

Cosmic rays (CRs) in the Galaxy are an important dynamical component of the interstellar medium (ISM) that interact with the other major components (interstellar magnetic and radiation fields, and gas) to produce broadband interstellar emissions that span the electromagnetic spectrum. The standard modelling of CR propagation and production of the associated emissions is based on a steady-state assumption, where the CR source spatial density is described using a smoothly varying function of position that does not evolve with time. While this is a convenient approximation, reality is otherwise where primary CRs are produced in and about highly localised regions, e.g., supernova remnants, which have finite lifetimes. In this paper we use the latest version of the GALPROP CR propagation code to model time-dependent CR injection and propagation through the ISM from a realistic three-dimensional discretised CR source density distribution, together with full three-dimensional models for the other major ISM components, and make predictions of the associated broadband non-thermal emissions. We compare the predictions for the discretised and equivalent steady-state model, finding that the former predicts novel features in the broadband non-thermal emissions that are absent for the steady-state case. Some of features predicted by the discretised model may be observable in all-sky observations made by WMAP and Planck, the recently launched eROSITA, the Fermi-LAT, and ground-based observations by HESS, HAWC, and the forthcoming CTA. The non-thermal emissions predicted by the discretised model may also provide explanations of puzzling anomalies in high-energy gamma ray data, such as the Fermi-LAT north/south asymmetry and residuals like the so-called "Fermi bubbles".

arXiv commentAccepted version. Published online Dec 26: ApJ 887, 250 (2019). 22 pages, 14 figures, 2 movies. Movies and configuration files available at the GALPROP website: https://galprop.stanford.edu/

References in corpus (66)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results
• Fermi Large Area Telescope Second Source Catalog
• Cosmic-ray propagation and interactions in the Galaxy
• Propagation of cosmic-ray nucleons in the Galaxy
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Radioactive 26Al and massive stars in the Galaxy
• Fermi-LAT Observations of the Diffuse Gamma-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium
• Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• The H.E.S.S. Galactic plane survey
• Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data
• Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center
• X-ray background measurements with XMM-Newton EPIC
• The 2HWC HAWC Observatory Gamma Ray Catalog
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Deriving global structure of the Galactic Magnetic Field from Faraday Rotation Measures of extragalactic sources
• Hydromagnetic turbulence in computer simulations
• Extended Anomalous Foreground Emission in the WMAP 3-Year Data
• The Most Likely Sources of High Energy Cosmic-Ray Electrons in Supernova Remnants
• Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
• Attenuation of VHE gamma rays by the Milky Way interstellar radiation field
• Revisiting the radial distribution of pulsars in the Galaxy
• A Measurement of the Spatial Distribution of Diffuse TeV Gamma Ray Emission from the Galactic Plane with Milagro
• Galactic synchrotron emission with cosmic ray propagation models
• Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
• Solution of heliospheric propagation: unveiling the local interstellar spectra of cosmic ray species
• Very high energy particle acceleration powered by the jets of the microquasar SS 433
• Analytic Solution for Self-regulated Collective Escape of Cosmic Rays from their Acceleration Sites
• High-Energy Gamma Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium
• Self-Generated Cosmic-Ray Confinement in TeV Halos: Implications for TeV Gamma-Ray Emission and the Positron Excess
• Anisotropic inverse Compton scattering in the Galaxy
• Diffuse Galactic gamma ray flux at very high energy
• Origin of the Cosmic Ray Galactic Halo Driven by Advected Turbulence and Self-Generated Waves
• Diffuse Galactic gamma-ray emission with H.E.S.S
• Non-linear diffusion of cosmic rays escaping from supernova remnants - I. The effect of neutrals
• TeV Halos are Everywhere: Prospects for New Discoveries
• Cosmic-ray protons, nuclei, electrons, and antiparticles under a two-halo scenario of diffusive propagation
• Polarised radio filaments outside the Galactic plane
• Propagation of Cosmic Rays in Heliosphere: the HelMod Model
• A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
• The Three-Dimensional Spatial Distribution of Interstellar Gas in the Milky Way: Implications for Cosmic Rays and High-Energy Gamma-Ray Emissions
• Cosmic rays, gas and dust in nearby anticentre clouds : I -- CO-to-H2 conversion factors and dust opacities
• Fermi LAT study of cosmic-rays and the interstellar medium in nearby molecular clouds
• Cosmic-Ray Propagation in Light of Recent Observation of Geminga
• Deciphering the local Interstellar spectra of primary cosmic ray species with HelMod
• HelMod in the works: from direct observations to the local interstellar spectrum of cosmic-ray electrons
• Cosmic-ray propagation properties for an origin in SNRs
• Synthetic simulations of the extragalactic sky seen by eROSITA. I. Pre-launch selection functions from Monte-Carlo simulations
• Fermi-LAT Observations of Gamma-Ray Emission Towards the Outer Halo of M31
• Multi-messenger gamma-ray counterpart of the IceCube neutrino signal
• Cosmic ray electrons and the diffuse gamma ray spectrum
• Cosmic ray electrons and positrons from discrete stochastic sources
• Loops and spurs: The angular power spectrum of the Galactic synchrotron background
• Stochastic cosmic ray sources and the TeV break in the all-electron spectrum
• Escape of cosmic rays from the Galaxy and effects on the circumgalactic medium
• Stable laws and cosmic ray physics
• Variance of the Galactic nuclei cosmic ray flux
• Galactic PeVatrons and helping to find them: Effects of Galactic absorption on the observed spectra of very high energy $\gamma$-ray sources
• Systematic effects in the extraction of the 'WMAP haze'
• The effects of discreteness of galactic cosmic rays sources
• A stochastic simulation of the propagation of Galactic cosmic rays reflecting the discreteness of cosmic ray sources. Age and path length distribution
• Quantifying the Interstellar Medium and Cosmic Rays in the MBM 53, 54, and 55 Molecular Clouds and the Pegasus Loop using Fermi-LAT Gamma-ray Observations

Cited by in corpus (17)

• Inference of the Local Interstellar Spectra of Cosmic Ray Nuclei Z<=28 with the GalProp-HelMod Framework
• Deciphering the local Interstellar spectra of secondary nuclei with GALPROP/HelMod framework and a hint for primary lithium in cosmic rays
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Simulations of cosmic ray propagation
• Where are Milky Way's Hadronic PeVatrons?
• On the origin of observed cosmic ray spectrum below 100 TV
• Population synthesis of pulsar wind nebulae and pulsar halos in the Milky Way -- Predicted contributions to the very-high-energy sky
• The Steady-State Multi-TeV Diffuse Gamma-Ray Emission Predicted with GALPROP and Prospects for the Cherenkov Telescope Array
• On the surface brightness radial profile of the extended $\gamma$-ray sources
• The rigidity dependence of galactic cosmic-ray fluxes and its connection with the diffusion coefficient
• Cosmic-ray propagation under consideration of a spatially resolved source distribution
• Signatures of Recent Cosmic-Ray Acceleration in the High-Latitude $\gamma$-Ray Sky
• Current status and desired accuracy of the isotopic production cross-sections relevant to astrophysics of cosmic rays II. Fluorine to Silicon (and updated LiBeB)
• Investigating the CREDIT history of supernova remnants as cosmic-ray sources
• The GALPROP Cosmic-ray Propagation and Non-thermal Emissions Framework: Release v57
• Cosmic Radioactivity and Galactic Chemical Evolution
• SECRET: Stochasticity Emulator for Cosmic Ray Electrons