Anomalous Distributions of Primary Cosmic Rays as Evidence for Time-dependent Particle Acceleration in Supernova Remnants
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 lincar 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 increasc of energy,which may be responsible for the ”knee” of CRs.
acceleration of particles cosmic rays ISM:supernova remnants shock waves Supporting material:data behind figure
Yiran Zhang Siming Liu Qiang Yuan
Key Laboratory of Dark Matter and Space Astronomy,Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210008,China;School of Astronomy and Space Science,University of Science and Technology of China,Hefei 230026,Anhui,China
国内会议
第8届高海拔宇宙线探测国际研讨会(The 8th International Workshop on Air Shower Detection At High Altitudes)
上海
英文
1-20
2017-12-10（万方平台首次上网日期，不代表论文的发表时间）