| Supernova remnants(SNRs)and Pulsar Wind Nebulae(PWNe)are important gamma ray sources in the Galaxy and candidates for the origin of Galactic cosmic rays(GCRs).It is usually assumed that SNRs evolve in the uniform medium of the Galaxy,particles(or GCRs)inside a SNR are accelerated to extremely high energy through the nonlinear diffusion shock acceleration(NDSA),and some of them escape from the SNRs and propagate in the Galaxy.However,the observations show that the realistic medium around the SNR may be turbulent,and has an important role in both the SNR evolution and particle acceleration.On the other hand,as one of three types of SNRs(i.e.,plerions),Crab Nebula are observed to emit non-thermal photons from radio to gamma-ray energy bands,particularly to Pe V energy,which provide important information for studying the origin of high energy radiation.In this thesis,following two topics are investigated: the dynamical properties of young type Ia SNRs in a turbulent medium,and high energy photon emission from the Crab Nebula,in particular the origin of possible Pe V radiation.In the study of evolution of the SNR in the turbulent medium,firstly,the assumption of the uniform medium around the SNR is abandoned,a realistic medium is taken into account: both density field and magnetic field are turbulent and satisfy Kolmogorov-like power spectra.And then,the dynamical feedback effect of the accelerated particles in the SNR is considered through a time-dependent effective adiabatic index.On this basis,the dynamical properties of young type Ia SNRs in the turbulent medium are simulated by using the magnetohydrodynamic model in two-dimensional cylindrical coordinates.Main results in our simulations are as follows:(1)compared to the uniform medium case and the effective adiabatic index is not considered,there is a rippled forward shock and distorted reverse shock,a thinner shocked ejecta layer and a denser,narrower intershock region are present after considering the dynamical feedback of accelerating particles and a turbulent medium,the net effect is that there is a higher density difference between the shocked ejecta and the shocked interstellar medium,resulting in a rapid growth of Rayleigh-Taylor instability;(2)the maximum magnetic field occurs not only at the contact discontinuity,but also near the immediate downstream of the shock,and the maximum magnetic field increases with time rapidly and its spatial location is close the immediate downstream of the shock,indicating that a strongly amplified magnetic field appears there;and(3)the relative contact discontinuity positions coincides with the X ray observations of two typical supernova remains SN 1006 and Tycho,representing the simulation results are reasonable.In the investigation of non-thermal photon emission from the Crab Nebula,the multi-band photon radiation are considered in a spatially-dependent lepto-hadronic model for the PWN.In this model,the PWN is assumed to evolves in the approximation of the spherical symmetry and the particles are injected at the termination shock(TS),the spectral energy distributions(SEDs)of photons are obtained by solving the FokkerPlank equations of particles and the photon conservation equation.Main results are as follows:(1)our calculated multi-band photon SED can reproduce the observed date of the Crab Nebula well;(2)The SED from radio to ~100 Te V bands can be explained by the synchrotron and IC scattering processes of relativistic electrons,while at 100 Pe V energy region,the γ-rays produced in π0decay of proton-proton interaction have an important contribution,which depends on the number density of surrounding medium,indicating that Crab Nebula may be one of GCR Pevtrons;and(3)at different bands,the predicted changes of the spectral index with the radial distance are various,while the surface brightness decrease with the radial distance,which can be checked in future observations. |
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