Spiral Arms as Cosmic Ray Source Distributions

Abstract

There is evidence that the distribution of suspected cosmic ray sources are associated with the spiral arm structure of galaxies. It is yet not clearly understood what effect such a cosmic ray source distribution has on the particle transport in our Galaxy. We use the PICARD code to perform high-resolution 3D simulations of electrons and protons in galactic propagation scenarios that include four-arm and two-arm logarithmic spiral cosmic ray source distributions with and without a central bar structure as well as the spiral arm configuration of the NE2001 model for the distribution of free electrons in the Milky Way. Results of these simulation are compared to an axisymmetric radial source distribution. Also, effects on the cosmic ray flux and spectra due to different positions of the Earth relative to the spiral structure are studied. We find that high energy electrons are strongly confined to their sources and the obtained spectra largely depend on the Earth's position relative to the spiral arms. Similar finding have been obtained for low energy protons and electrons albeit at smaller magnitude. We find that even fractional contributions of a spiral arm component to the total cosmic ray source distribution influences the spectra on the Earth. This is apparent when compared to an axisymmetric radial source distribution as well as with respect to the Earth's position relative to the spiral arm structure. We demonstrate that the presence of a Galactic bar manifests itself as an overall excess of low energy electrons at the Earth. Using a spiral arm geometry as a cosmic ray source distributions offers a genuine new quality of modelling and is used to explain features in cosmic ray spectra at the Earth that are else-wise attributed to other propagation effects. We show that realistic cosmic ray propagation scenarios have to acknowledge non-axisymmetric source distributions.[Abbreviated]

50 pages, 13 figures, accepted for publication in Astroparticle Physics

References in corpus (7)

• Observation of an anomalous positron abundance in the cosmic radiation
• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis
• Global cosmic-ray related luminosity and energy budget of the Milky Way
• Measurements of cosmic-ray secondary nuclei at high energies with the first flight of the CREAM balloon-borne experiment
• Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
• Measurement of cosmic-ray low-energy antiproton spectrum with the first BESS-Polar Antarctic flight

Cited by in corpus (8)

• Cosmic-ray propagation with DRAGON2: I. numerical solver and astrophysical ingredients
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• A Hitch-hiker's Guide to Stochastic Differential Equations: Solution Methods for Energetic Particle Transport in Space Physics and Astrophysics
• Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
• Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using PICARD
• Reconciling the diffuse Galactic gamma-ray and the cosmic ray spectra
• Diffuse Gamma Rays in 3D Galactic Cosmic-ray Propagation Models
• The Use Case of a New ISRF on Diffuse Gamma-ray Emission Models