多數位於星系內之X光天體均屬變星抑或瞬變星，目前尚未確知其變化會否造成該星系之X光光度函式測量上之變化。此文乃以NGC7331星系為例，以錢德拉X光望遠鏡七次之觀測資料為本，希能探究此一問題。如採用指數為1.7之冪律光譜模型，此研究在0.3至0.8千電子伏特之能量範圍的探測極限，估計為每秒7×10^37爾格。本研究探測得五十五X光點光源，其中十三者爲變星，三者為瞬變星，並有些許具有X光雙星常見之雙狀態變化現象。與前針對同星系之研究相較，多發現九個超亮X光光源，且此五十五者中八者疑為低質量或高質量X光雙星。本研究採用哈伯望遠鏡於前述在本星系尋得之X光光源位置，希能覓得其可見光相對應天體，共得二十又一者，惜因無法排除純為巧合之因素，其真確尚未能知。據本研究超新星2014C光譜分析，估算出其周圍中性氫柱狀密度與時俱減，其產生之低能量光子同其外殼擴張則與時俱增。本研究首次採用貝氏統計法估算此星系之X光光度函式，於七次觀測資料中覓得其最佳函式模型應為具有指數截止的冪律分布，指數約0.5且截止能量為每秒8×10^38爾格。本研究足證多時期之觀測，可減明亮變星於星系光度函式測量之誤判。

X-ray point sources in galaxies are dominated by X-ray binaries (XRBs) that are vari- ables or transients and whether their variability would alter the X-ray luminosity functions (XLF) is still in debate. Here we report on NGC 7331 as an example to test this with 7 Chandra observations. Their detection limit is 7×10^37 erg s^−1 in the 0.3 – 8.0 keV energy range by assuming a power-law spectral model with a photon index of 1.7. We detected 55 X-ray sources. Thirteen of them are variables for which 3 of them are transients and some of the sources possess a bimodal luminosity-hardness ratio feature, which is often observed among X-ray binaries. Nine more ultra-luminous X-ray sources are found comparing to previous studies and 8 are likely to be low-mass or high-mass XRBs. Twenty-one optical counterpart candidates are found based on the Hubble Space Telescope images, but we can- not rule out the possibility of positional coincidence. The spectral analysis of SN 2014C shows a trend of increasing soft photons and decreasing hydrogen column densities as its outer shell expands. We fit the 7 incompleteness-corrected XLFs to both a power-law (PL) and a power-law with an exponential cut-off (PLC) model using Bayesian method, which is the first time used in XLF fitting. The hierarchical PLC model can describe the XLF of NGC 7331 best with a slope of ∼ 0.5 and a luminosity cut-off around 8×10^38 erg s^−1. This study proves that multi-epoch observations decrease the deviation due to the variable luminous sources in XLFs.

List of figures .................................... viii
List of tables ....................................... ix
1 Introduction ...................................................... 1
1.1 Nearby galactic X-ray point sources as seen by Chandra .......... 1
1.1.1 X-ray binaries................................................. 2
1.1.2 Ultraluminous X-ray sources.................................... 3
1.1.3 Supernova and supernova remnant................................ 4
1.1.4 Active Galactic nucleus ....................................... 5
1.2 X-ray point source population study ............................. 6
1.3 Introduction of NGC7331 ......................................... 9
1.3.1 Star formation rate ........................................... 9
1.3.2 Metallicity and age........................................... 11
1.3.3 NGC7331 as seen in multi-wavelength .......................... 13
1.3.4 High-energy emitting objects in NGC7331 ...................... 15

2 X-ray point sources in NGC 7331 .................................. 21
2.1 Introduction.................................................... 21
2.2 X-ray data analysis ............................................ 21
2.2.1 Chandra observations ......................................... 21
2.2.2 Data reduction and point source detection .................... 22
2.2.3 Fluxes and variability........................................ 30
2.2.4 Colors and spectral fitting................................... 31
2.3 Optical analysis................................................ 36
2.3.1 Optical observations ......................................... 36
2.3.2 Astrometry ................................................... 39
2.3.3 Photometry of the optical sources in HST images .............. 41
2.3.4 Optical counterparts identification........................... 41
2.4 Discussion...................................................... 43

3 Population study of NGC 7331 ..................................... 47
3.1 X-ray luminosity function of galaxies .......................... 47
3.2 X-ray luminosity function of NGC7331 ........................... 48
3.2.1 Incompleteness correction .................................... 48
3.2.2 Introduction to Bayesian statistics .......................... 50
3.2.3 Using Bayesian inferences in X-ray luminosity function fitting 51
3.2.4 Results of X-ray luminosity function fitting ................. 54
3.3 Discussion ..................................................... 55

4 X-ray and optical analysis of SN 2014C ........................... 61
4.1 Introduction of SN2014C ........................................ 61
4.2 X-ray observation and analysis of SN2014C ...................... 64
4.2.1 Chandra and NuSTAR observations of SN2014C ................... 64
4.2.2 X-ray spectral fitting of SN2014C ............................ 64
4.3 Optical analysis of SN2014C .................................... 70
4.4 Discussion ..................................................... 75

5 Summary and future work .......................................... 77

References ......................................................... 79

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