| Since the discovery of cosmic rays(CRs)in 1912,the origin of these high energy particles remains one of the most controversial subject in astrophysics,and the gamma-ray emission produced by their interaction with the medium is the key to solve this mystery.Supernova remnant(SNR)is considered to be the most probable accelerator of Galactic CRs(GCRs)for the huge amounts of kinetic energy attained from the supernova explosion.Aiming at a better understanding of the relation between SNRs and GCRs as well as the acceleration and propagation process of high energy particles,we selected several SNRs that are very likely located in the molecular environment and performed comprehensive study mainly based on the data analyses of gamma-ray observation from Fermi Large Area Telescope(LAT)along with multi-wavelength ob-servations.In Chapter 1,we briefly reviewed the connection between SNRs and the origin of GCRs,the production and observation of gamma-rays,the structure and performance of Fermi-LAT as well as the data analysis methods.In Chapter 2,we presented our study of the thermal composite SNR Kes 41 based on GeV gamma-ray observation.A point-like gamma-ray source with a significance of 24? in the energy range of 0.2-300 GeV,was detected to the northwest of Kes 41 where located the MC that interacting with the SNR.Hadronic interactions among the high energy protons escaped from Kes41 and the nearby MC could naturally explain the morphology and the spectrum of these gamma-rays.Since no obvious variability or pulse was found from this source,and the leptonic scenario requires an unreasonable energy budget of electrons to reproduce the gamma-ray spectrum,this source is unlikely to be a pulsar.Besides,we also presented a brief discussion of Kes 41 within the context of other thermal composite SNRs that have been detected at y-ray energies.We found that the gamma-rays from these SNRs usually show the feature of hadronic emission,most of these SNRs are interacting with MCs.In Chapter 3,we reported our research on SNR Kes 73 that harbors the magnetar 1E 1841-045 based on Fermi-LAT data and the CO-line observation data.We detected an extended gamma-ray source located on the west of Kes 73 with a significance of 21.6 ? in 0.1-300 GeV range.By the CO data analyses,we discovered the interaction between Kes 73 and the MC at local standard of rest velocity?90 km s-1,and the evidence includes the intensity ratio of 12CO(J=2-1)to 12CO(J=1-0)which is>1 and the morphological consistency.We also obtained the kinematic distance of Kes 73?9 kpc.Moreover,the gamma-ray spectrum cannot be simply reproduced by leptonic emission or by emission that totally generated 1E 1841-045.The hadronic emission component is necessary,and the associated MC could provide enough targets for the accelerated protons to collide with.Besides,we found the magnetar might provide some low energy gamma-rays below?30 GeV,and provided the possibly gamma-ray spectrum of the magnetar from modeling the observation data.In Chapter 4,we revisited the star-forming region W30 to study the gamma-ray emission that possibly associated with SNR G8.7-0.1 Through spatial and spectral analyses,we revealed the cause of the energy-dependent distribution of the diffuse gamma-rays in this region,which is the overlap of two extended sources with different origins.One named as W30 that mostly overlaps with G8.7-0.1 has a softer spectrum that is similar to the spectra of middle-aged SNRs interacting with MCs.And this gamma-ray source is very likely generated from the protons accelerated by G8.7-0.1 interacting with surrounding dense MCs.The other has a harder spectrum and shows remarkable spatial and spectral consistency with the TeV emission from HESS J1804-216.A pulsar wind nebula powered by PSR J1803-2137 could be a natural explanation for the GeV-TeV gamma-rays from HESS J1804-216.In Chapter 5,we summarized the main results of our research and showed the prospect of future projects for gamma-ray observation. |
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