The Contribution Of Accelerated Particles In Supernova Remnants To Galactic Cosmic Rays

The origin,acceleration,and propagation of cosmic rays are key topics in the field of high energy astrophysics.It has been believed that supernova remnants(SNRs)are the most likely source for a long time,but the acceleration and escape of the particles in the SNRs are still open questions.Since both protons(H)and helium(He)nuclei are the most abundant components of Galactic cosmic rays,studying their properties will help us to further understand the origin,acceleration and propagation of cosmic rays.In this thesis,based on the study of the acceleration and escape of particles in the SNRs,we investigated the spectral properties of cosmic H+He nuclei around the”knee”region and the spectral hardening of cosmic ray protons and helium nuclei near200 Ge V,respectively.The main results are as follows.We proposed a possible explanation of the knee of cosmic light component spec-trum from 100 Te V to 3 Pe V.The spectrum of cosmic rays exist a break around?3×10¹⁵e V,which is called as the”knee”and is one of the biggest questions in cosmic ray as-trophysics.Recent precise measurements of ARGO-YBJ?LHAASO showed that the“knee”of mixed spectrum of cosmic ray hydrogen and helium appeared at energy?700 Te V,a factor?0.2 of the previous result.Based on the nonlinear diffusion shock acceleration models,which taking the dynamic feedback of cosmic ray pressure on the shock and the magnetic field amplification into consideration,we use a semi-analytic approach to calculate the spectrum of accelerated particles,in the assumption that a quasi-stationary situation is reached at any given time.We find that a large acceleration efficiency can lead to a steeping in the spectrum of the accelerated particles.And the different position of the free escape boundary and the circumstellar environment could produce different maximum energy of the particles which escaping form far upstream during the early stages of the supernova remnant evolution.The observed spectrum of the“knee”of mixed spectrum of H+He measured by the ARGO-YBJ?LHAASO can be well reproduced by this model.We explained the spectral hardening of cosmic ray protons and helium nuclei in at about 200 Ge V.The cosmic ray spectrum can not be described by a single power law below the knee.The recent observation of PAMELA,AMS-02 and CREAM showed that the spectrum of cosmic ray proton and helium nuclei became hardening at around200 Ge V/nucleon.Using the model of Galactic cosmic rays accelerated in supernova remnant proposed by Bell(2015)and based on the nonlinear diffusion acceleration in supernova remnant,we assume that the particles injected into the interstellar medium from the supernova remnant can be described by a two-component particle spectrum:the high-energy population is dominated by the particles with energies above 200 Ge V released upstream of the shock of supernova remnants,and the low-energy population is attributed to the particles with energies below 200 Ge V advected downstream of the shock of supernova remnants.The model can well explain the spectrum hardening of cosmic ray proton and helium at 200 Ge V,indicating that such feature is caused by the different distribution of the accelerated particles in the upstream and downstream regions of the shock.Our studies indicate that the supernova remnant is the most likely source of galactic cosmic rays,which can explain the spectral characteristics of the Galactic cosmic rays proton and helium nuclei.The thesis is organized as follows:in Chapter one,we give a brief introduction about cosmic rays and supernova remnants.In Chapter two,we briefly review the acceleration models of supernova remnants.In Chapter three,based on the nonlinear diffusion shock acceleration model,we explain the knee feature of cosmic proton and helium nuclei observed by ARGO-YBJ?LHAASO.In Chapter four,we explain the spectral hardening of cosmic ray proton and helium nuclei at energy about200 Ge V.A brief conclusions and discussion are given in Chapter five.