| Summary: | 碩士 === 國立臺灣大學 === 物理學研究所 === 104 === Unveiling the nature of accretion process onto the supermassive black hole (SMBH) is one of the primary purposes in modern high energy astrophysics. Constraining mass accretion rate (M ̇ ) can not only clarify the features of in- flow but also connect to the dynamics of outflow. In this dissertation, we concentrate on the low-luminosity active galactic nuclei (LLAGN) of Cygnus A, which are thought to be powered by radiatively inefficient accretion flow (RIAF). Faraday rotation measure (RM), the tracer of plasma density, pro- vides a powerful tool that can be used to investigate the mass accretion rate near the SMBH of LLAGN. We present the polarimetric observation results towards Cygnus A utilizing Submillimeter Array at 230 GHz and obtain the observational constraint on RM. With the scenarios of beam/bandwidth de- polarization and advection-dominated accretion flow model fitting, the mass accretion rate and the accretion type of Cygnus A can be constrained, and the convection-dominated accretion flow solution is excluded.
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