超新星殘骸的多波段特性分析

Abstract

本論文為大麥哲倫星系中超新星殘骸特性的系統性研究。大麥哲倫星系距離已知，且內部消光低，因此提供了研究超新星殘骸的良好機會。第一部分，我們呈現超新星殘骸X射線光度與大小分布圖中幾個有趣的群聚現象：（1）小（數至10秒差距）的超新星殘骸，主要是X射線光度超過每秒$10^{36}$耳格的Ia型超新星殘骸。小的核心坍縮超新星殘骸之所以缺乏，是由於此類超新星爆發於其母恆星吹出的星際氣泡之內，而氣泡內密度相當低。（2）中等尺寸（10至30秒差距）的核心坍縮超新星殘骸，在X射線光度上呈現兩極化的分布。X射線明亮的超新星殘骸，處在具有分子雲的環境中，或者本身擁有脈衝星風星雲；X射線暗淡的超新星殘骸則位在低密度的星際環境中。第二部分，我們說明，傳統上識別Ia型超新星殘骸的流程，並不適用於比麥哲倫雲更遠的星系。且多數Ia型超新星殘骸，由於巴爾麥主導的 譜線特徵，被超新星殘骸的識別判準排除在外。為建立識別年輕Ia型（特別是巴爾麥主導的）超新星殘骸的方法，我們用大麥哲倫星系的超新星殘骸樣本，來探討年輕Ia型超新星殘骸的特性。我們提出，X射線光度每秒$10^{36}-10^{37}$耳格、在可見光呈小而球殼狀的型態、老的恆星與星際環境，可作為幫助識別年輕Ia型超新星殘骸的特徵。利用這些特徵，我們建立了在較遠星系尋找Ia型超新星殘骸的一套新方法。

This thesis presents a systematical study of the characteristics of SNRs in the Large Magellanic Cloud (LMC). Due to the known distance and low internal extinction, the LMC provides us great opportunities to study supernova remnants (SNRs). In Part I, we show some interesting groupings in the X-ray luminosity ($L_X$) and size diagram of SNRs: (1) Small LMC SNRs, a few to 10 pc in size, are dominated by Type Ia with $L_X > 10^{36}$ ergs s$^{−1}$. The scarcity of small core-collapse (CC) SNRs is a result of CCSNe exploding in the low-density interiors of interstellar bubbles blown by their massive progenitors. (2) Medium-sized (10-30 pc) CC SNRs show bifurcation in $L_X$, with the X-ray-bright SNRs either in an environment associated with molecular clouds or containing pulsar wind nebulae, and the X-ray-faint SNRs being located in low-density interstellar environments. In Part II, we show that the conventional procedure of identification of Type Ia SNRs is not applicable in galaxies more distant than the Magellanic Clouds, and most Type Ia SNRs are excluded by the criteria of SNR identifications because of their Balmer-dominated line feature. To build up methods to identify young Type Ia, especially Balmer-dominated, SNRs in more distant galaxies, we use the LMC SNR sample to investigate the characteristics of young Type Ia SNRs. We suggest that the $L_X$ in the range $10^{36}-10^{37}$ ergs s$^{−1}$, optical morphology of small round shells, and old stellar and interstellar environments can be treated as the diagnostics to help us identify young Type Ia SNRs. With these characteristics, we establish a new methodology for searching for Type Ia SNRs in the more distant galaxies.