Dynamical Evolution Of Supernova Remnants And Their Morphologies Of Emission

Supernova remnants (SNRs), which are the relics of supernovae, carry large amounts of kinetic energy, and they are the important sources of particle accel-eration and nonthermal emission with energies from radio to very high-energy (VHE)7-rays in the Galaxy. Studies on the supernova remnants, which can help us further understand the burst mechanism of supernovae, the properties of the medium around the progenitors, the formation of pulsars and their nebulae, the synthesis of heavy nuclei, the physics of shocks and particle acceleration, and the production of high-energy emission, belong to the hot topics of both theoretical and observational researches.The particle acceleration, radiative mechanisms, and the morphologies of emission involved in supernova remnants depend heavily on the initial conditions of the supernovae and the ambient interstellar matter, and it results in the ob-served radiative features and the morphologies for supernova remnants are great different with each other. The dynamical evolution and the morphologies of emis-sion are investigated in this dissertation, and the structure and the main contains are as follows.The history of researches on SNRs and hot topics are briefly reviewed, and the observed results of X-ray satellite Chandra and the VHD γ-ray Cherenkov telescopes, the observed features of the multiband spectra and the morphologies of emission for supernova remnants are summarized in Chapter1.In Chapter2, firstly, the basic conservation equations in the hydrodynamics and MHD, which contain the mass conservation, the momentum conservation, the energy conservation, and the transportation of small perturbations, are briefly in-troduced. Secondly, the shock acceleration at the nonrelativistic shocks, the test particle theory of the shock acceleration, the nonlinear diffusive shock acceler-ation, and the results from numerical simulations are summarized. Thirdly, the production processes, which contain synchrotron radiation, inverse Compton scat-tering and pp interaction, of the nonthermal emission from supernova remnants are introduced.In Chapter3, firstly, the results from numerical simulation are indicated. The initial conditions for the simulations are shown, and the distributions of the den-sity, magnetic field, pressure, and the production of the instability in the dynamical evolution from the2D simulation are illustrated. A shock which is produced as the ejecta with high-velocity transported in the interstellar medium heat the medium, and then a two-shock structure is produced when a reverse shock is formed to hear the supernova ejecta. A surface of contact discontinuity is located between the two shocks, and the Rayleigh-Taylor instability is triggered with enhanced magnetic field. Secondly, the numerical model is extended to three dimension, and the dynamical features of the supernova remnant evolved both in uniform or in turbulent medium are studied. Finally, we investigate detailed the dynamical properties and morphologies of emission for the supernova remnants SN1006and RX J0852.0-4622. The observations their morphologies have unsymmetrical struc-tures. For example, the multi-band morphologies of nonthermal emission from SN1006show that the remnant is bright in the northeastern and southwestern parts, and the images are not strictly symmetrical with knots and filaments along the shell; moreover, the observations in X-rays and γ-rays indicate the morphologies of emission from RX J0852.0-4622are unsymmetrical with irregularities. The shell is broken at some places with weak emission, and bright at the other places. For example, three bright regions are located to the north of the remnant. We obtain the morphologies of emission, shock velocity via the MHD simulation with the theory of the shock acceleration, and the morphologies are compared with the observations. The results show that the detected features of the morphologies can-not be explained with the remnants evolved in the uniform medium. On the other hand, the unsymmetrical can be produced by assuming the remnants are evolved in the turbulent medium. and the results are consistent with the observations.Some summarizations and the conclusions are firstly given in Chapter4. The density, magnetic field and pressure for the remnants evolved in different back-grounds are obtained using the2D/3D MHD simulations. Moreover, combined with the theories of the shock acceleration and radiation mechanisms, the mor-phologies of emission for the remnants can be obtained to directly comparison with the observations. The morphologies of emission for SN1006and RX J0852.0-4622are studies in detail, and the main conclusions are (1) the observed morphologies can be reproduced by assuming the turbulent background in the regime of diffu-sive shock acceleration;(2) for SN1006, the large bump on the NE limb can be explained as a result of a lower-density region, which has a radius of about2.5pc and a density of about0.4times of the general ambient medium, swept by the shock front, and the other smaller ones on the SW limb can either be reproduced with smaller regions with lower-densities swept by the shock or be explained as the protrusions in the scenario of the efficient cosmic ray acceleration when the instability fingers effectively overtake the forward shock. Finally, some unresolved questions on supernova remnants and our future research topics are indicated.