THE LONG-TERM VARIABILITY OF THE X-RAY SOURCES IN M82

星系M82中X光源的長時間尺度變化

江奕寬(Yi-Kuan Chiang)

指導教授 ： 江國興

國立清華大學/理學院/天文研究所/碩士(2009年)

摘要

本論文研究星系M82中X光源在長時間尺度下的變化。透過分析自1999至2007年間9個錢卓拉X光望遠鏡對M82觀測的資料，我們在M82內偵測到58個亮度約大於1037 ergs s-1 的X光點光源。在這58個X光源中，我們發現了三個可能與超星星殘骸有關的X光源，以及一個超軟X光源。在長時間尺度下，29個X光源有亮度的變化，3個X光源有光譜的變化。更進一步的，我們將29個X光源歸類為變星，8個歸類為恆定光源。在這29個變星之中，有20個光源的光度變化比率大於3倍，有6個變化劇烈的光源被歸類為瞬變現象。星系M82中，54%的X光源在長時間尺度下的光度變化比率大於3倍，與其他星系相較之下，這樣的光變是極為強烈的。如此強烈的長時間尺度光變，意味著在M82中的X光源大多為X光雙星。此外，我們發現M82中的一個超新星SN 2004am，在超新星爆炸後的幾年內，X光亮度穩定增加。截至目前為止，只有兩個超新星，SN 1996cr和SN 1987A被觀測到類似的現象。透過研究與比較這三個超新星，也許可以推知環繞超新星物質的密度以及其結構。探知SN 2004am的本質可以增加我們對II型超新星末期演化的了解。因此，我們對錢卓拉X光望遠鏡提出一個觀測提案，藉以更進一步的研究超新星SN 2004am。

關鍵字

天文 ； X光 ； 星系

並列摘要

We investigate the long-term variability exhibited by the X-ray point sources in the starburst galaxy M82. By combining 9 Chandra observations taken between 1999 and 2007, we detect 58 X-ray point sources within the D25 isophote of M82 down to a luminosity of ~ 1037 ergs s-1. Of these 58 sources, we identify 3 supernova remnant candidates and one supersoft source. Twenty-nine sources in M82 exhibit long-term (i.e., days to years) flux variability and 3 show long-term spectral variability. Furthermore, we classify 29 sources as variables and 8 as persistent sources. Among the total 29 variables, 20 varied by a flux ratio of > 3 and 6 are transient candidates. By comparing with other nearby galaxies, M82 shows extremely strong long-term X-ray variability that 54% of the X-ray sources are variables with a flux ratio of > 3. The strong X-ray variability of M82 suggests that the population is dominated by X-ray binaries. Besides, one of the X-ray supernovae we found, SN 2004am, shows rising X-ray flux for several years after explosion. There are only two supernovae, SN 1996cr and SN 1987A, which have similar long-term X-ray light curve. By comparing SN 2004am with SN 1996cr and SN 1987A, we might be able to gain valuable information about the circumstellar matter density structure. Hence, confirming the nature of SN 2004am will add an important sample in studying late-time behaviors of Type II supernovae. New follow-up Chandra observations would be useful to constrain the nature. Therefore, we present a proposed Chandra observation to monitor SN 2004am.

並列關鍵字

Astronomy ； X-ray ； Galaxy

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