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Title: Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants

Abstract

Recent precise measurements of cosmic-ray (CR) spectra show that the energy distribution of protons is softer than those of heavier nuclei, and there are spectral hardenings for all nuclear compositions above ∼200 GV. Models proposed for these anomalies generally assume steady-state solutions of the particle acceleration process. We show that if the diffusion coefficient has a weak dependence on the particle rigidity near shock fronts of supernova remnants (SNRs), time-dependent solutions of the linear diffusive shock acceleration at two stages of SNR evolution can naturally account for these anomalies. The high-energy component of CRs is dominated by acceleration in the free expansion and adiabatic phases with enriched heavy elements and a high shock speed. The low-energy component may be attributed to acceleration by slow shocks propagating in dense molecular clouds with low metallicity in the radiative phase. Instead of a single power-law distribution, the spectra of time-dependent solutions soften gradually with the increase of energy, which may be responsible for the “knee” of CRs.

Authors:
; ;  [1]
  1. Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
Publication Date:
OSTI Identifier:
22654434
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 844; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; CLOUDS; DIFFUSION; DISTRIBUTION; ENERGY SPECTRA; EXPANSION; HEAVY NUCLEI; METALLICITY; PARTICLES; PRIMARY COSMIC RADIATION; PROTONS; SHOCK WAVES; SPECTRAL HARDENING; STEADY-STATE CONDITIONS; SUPERNOVA REMNANTS; TIME DEPENDENCE; VELOCITY

Citation Formats

Zhang, Yiran, Liu, Siming, and Yuan, Qiang, E-mail: liusm@pmo.ac.cn. Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA7DE1.
Zhang, Yiran, Liu, Siming, & Yuan, Qiang, E-mail: liusm@pmo.ac.cn. Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants. United States. doi:10.3847/2041-8213/AA7DE1.
Zhang, Yiran, Liu, Siming, and Yuan, Qiang, E-mail: liusm@pmo.ac.cn. Thu . "Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants". United States. doi:10.3847/2041-8213/AA7DE1.
@article{osti_22654434,
title = {Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants},
author = {Zhang, Yiran and Liu, Siming and Yuan, Qiang, E-mail: liusm@pmo.ac.cn},
abstractNote = {Recent precise measurements of cosmic-ray (CR) spectra show that the energy distribution of protons is softer than those of heavier nuclei, and there are spectral hardenings for all nuclear compositions above ∼200 GV. Models proposed for these anomalies generally assume steady-state solutions of the particle acceleration process. We show that if the diffusion coefficient has a weak dependence on the particle rigidity near shock fronts of supernova remnants (SNRs), time-dependent solutions of the linear diffusive shock acceleration at two stages of SNR evolution can naturally account for these anomalies. The high-energy component of CRs is dominated by acceleration in the free expansion and adiabatic phases with enriched heavy elements and a high shock speed. The low-energy component may be attributed to acceleration by slow shocks propagating in dense molecular clouds with low metallicity in the radiative phase. Instead of a single power-law distribution, the spectra of time-dependent solutions soften gradually with the increase of energy, which may be responsible for the “knee” of CRs.},
doi = {10.3847/2041-8213/AA7DE1},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 844,
place = {United States},
year = {Thu Jul 20 00:00:00 EDT 2017},
month = {Thu Jul 20 00:00:00 EDT 2017}
}