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Title: Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition

Abstract

In this paper we investigate the effect of stochasticity in the spatial and temporal distribution of supernova remnants on the spectrum and chemical composition of cosmic rays observed at Earth. The calculations are carried out for different choices of the diffusion coefficient D(E) experienced by cosmic rays during propagation in the Galaxy. In particular, at high energies we assume that D(E)∝E{sup δ}, with δ = 1/3 and δ = 0.6 being the reference scenarios. The large scale distribution of supernova remnants in the Galaxy is modeled following the distribution of pulsars, with and without accounting for the spiral structure of the Galaxy. We find that the stochastic fluctuations induced by the spatial and temporal distribution of supernovae, together with the effect of spallation of nuclei, lead to mild but sensible violations of the simple, leaky-box-inspired rule that the spectrum observed at Earth is N(E)∝E{sup −α} with α = γ+δ, where γ is the slope of the cosmic ray injection spectrum at the sources. Spallation of nuclei, even with the small rates appropriate for He, may account for small differences in spectral slopes between different nuclei, possibly providing an explanation for the recent CREAM observations. For δ = 1/3 we findmore » that the slope of the proton and helium spectra are ∼ 2.67 and ∼ 2.6 respectively (with fluctuations depending on the realization of source distribution) at energies around ∼ 1 TeV (to be compared with the measured values of 2.66±0.02 and 2.58±0.02). For δ = 0.6 the hardening of the He spectra is not observed. The stochastic effects discussed above cannot be found in ordinary propagation calculations, such as GALPROP, where these effects and the point like nature of the sources are not taken into account. We also comment on the effect of time dependence of the escape of cosmic rays from supernova remnants, and of a possible clustering of the sources in superbubbles. In a second paper we will discuss the implications of these different scenarios for the anisotropy of cosmic rays.« less

Authors:
;  [1]
  1. INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5 — 50125 Firenze (Italy)
Publication Date:
OSTI Identifier:
22280167
Resource Type:
Journal Article
Journal Name:
Journal of Cosmology and Astroparticle Physics
Additional Journal Information:
Journal Volume: 2012; Journal Issue: 01; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1475-7516
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; ASTROPHYSICS; CHEMICAL COMPOSITION; COMPARATIVE EVALUATIONS; COSMIC RADIATION; COSMIC RAY PROPAGATION; COSMOLOGY; FLUCTUATIONS; HELIUM; MILKY WAY; PROTONS; PULSARS; STOCHASTIC PROCESSES; SUPERNOVA REMNANTS; SUPERNOVAE; TEV RANGE; TIME DEPENDENCE

Citation Formats

Blasi, Pasquale, and Amato, Elena. Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition. United States: N. p., 2012. Web. doi:10.1088/1475-7516/2012/01/010.
Blasi, Pasquale, & Amato, Elena. Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition. United States. https://doi.org/10.1088/1475-7516/2012/01/010
Blasi, Pasquale, and Amato, Elena. 2012. "Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition". United States. https://doi.org/10.1088/1475-7516/2012/01/010.
@article{osti_22280167,
title = {Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition},
author = {Blasi, Pasquale and Amato, Elena},
abstractNote = {In this paper we investigate the effect of stochasticity in the spatial and temporal distribution of supernova remnants on the spectrum and chemical composition of cosmic rays observed at Earth. The calculations are carried out for different choices of the diffusion coefficient D(E) experienced by cosmic rays during propagation in the Galaxy. In particular, at high energies we assume that D(E)∝E{sup δ}, with δ = 1/3 and δ = 0.6 being the reference scenarios. The large scale distribution of supernova remnants in the Galaxy is modeled following the distribution of pulsars, with and without accounting for the spiral structure of the Galaxy. We find that the stochastic fluctuations induced by the spatial and temporal distribution of supernovae, together with the effect of spallation of nuclei, lead to mild but sensible violations of the simple, leaky-box-inspired rule that the spectrum observed at Earth is N(E)∝E{sup −α} with α = γ+δ, where γ is the slope of the cosmic ray injection spectrum at the sources. Spallation of nuclei, even with the small rates appropriate for He, may account for small differences in spectral slopes between different nuclei, possibly providing an explanation for the recent CREAM observations. For δ = 1/3 we find that the slope of the proton and helium spectra are ∼ 2.67 and ∼ 2.6 respectively (with fluctuations depending on the realization of source distribution) at energies around ∼ 1 TeV (to be compared with the measured values of 2.66±0.02 and 2.58±0.02). For δ = 0.6 the hardening of the He spectra is not observed. The stochastic effects discussed above cannot be found in ordinary propagation calculations, such as GALPROP, where these effects and the point like nature of the sources are not taken into account. We also comment on the effect of time dependence of the escape of cosmic rays from supernova remnants, and of a possible clustering of the sources in superbubbles. In a second paper we will discuss the implications of these different scenarios for the anisotropy of cosmic rays.},
doi = {10.1088/1475-7516/2012/01/010},
url = {https://www.osti.gov/biblio/22280167}, journal = {Journal of Cosmology and Astroparticle Physics},
issn = {1475-7516},
number = 01,
volume = 2012,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2012},
month = {Sun Jan 01 00:00:00 EST 2012}
}