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arXiv 1202.2358astro-ph.COastro-ph.HE
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探测环形星系NGC 1291的X射线双星

Probing the X-Ray Binary Populations of the Ring Galaxy NGC 1291

B. Luo, G. Fabbiano, T. Fragos, D. -W. Kim, K. Belczynski, N. J. Brassington, S. Pellegrini, P. Tzanavaris, Junfeng Wang, A. Zezas

备注：
15 pages, 11 figures. Accepted for publication in ApJ
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摘要：

我们提出了钱德拉研究的X射线二（XRB）人口的环状星系NGC 1291的凸起和环区域。我们检测到169个X射线点源的星系，75个在凸起和71个在环，利用四个可用的钱德拉观测总计有效曝光179 KS。我们报告的光度特性，这些来源的点源目录。约40%的核球源和约25%的环源的X射线计数率显示出>3σ的长期变异性。X射线的颜色表明，一个显着的部分（~75%）和环（~65%）的来源可能是低质量的X射线双星（LMXB）。核源的光谱表明，它是一个低光度活动星系核，具有中等的遮蔽度;在个别观测之间观察到光谱的变化。我们构造了0.3-8.0 keV的X射线光度函数（XLF）的隆起和环XRB人口，考虑到检测的不完整性和背景活动星系核污染。对于凸起和环形群体，我们分别达到~1.5 \times 10^{37}和~2.2 \times 10^{37} erg/s的90%完整性极限。两个XLF都可以用破幂律模型拟合，并且形状与LMXB占主导地位的种群的预期形状一致。我们在NGC 1291中对XRB种群进行了详细的种群合成建模，这表明所观察到的合并XLF由旧的LMXB种群主导。我们比较了膨胀和环XRB人口，并认为，环XRB与年轻的恒星星族比膨胀源，根据相对过密的X射线源在环中，一般硬X射线颜色的环源，在合并XLF的发光源过剩，和平坦的形状的环XLF。

英文摘要：

We present Chandra studies of the X-ray binary (XRB) populations in the bulge and ring regions of the ring galaxy NGC 1291. We detect 169 X-ray point sources in the galaxy, 75 in the bulge and 71 in the ring, utilizing the four available Chandra observations totaling an effective exposure of 179 ks. We report photometric properties of these sources in a point-source catalog. There are ~40% of the bulge sources and ~25% of the ring sources showing >3σlong-term variability in their X-ray count rate. The X-ray colors suggest that a significant fraction of the bulge (~75%) and ring (~65%) sources are likely low-mass X-ray binaries (LMXBs). The spectra of the nuclear source indicate that it is a low-luminosity AGN with moderate obscuration; spectral variability is observed between individual observations. We construct 0.3-8.0 keV X-ray luminosity functions (XLFs) for the bulge and ring XRB populations, taking into account the detection incompleteness and background AGN contamination. We reach 90% completeness limits of ~1.5\times10^{37} and ~2.2\times10^{37} erg/s for the bulge and ring populations, respectively. Both XLFs can be fit with a broken power-law model, and the shapes are consistent with those expected for populations dominated by LMXBs. We perform detailed population synthesis modeling of the XRB populations in NGC 1291, which suggests that the observed combined XLF is dominated by an old LMXB population. We compare the bulge and ring XRB populations, and argue that the ring XRBs are associated with a younger stellar population than the bulge sources, based on the relative overdensity of X-ray sources in the ring, the generally harder X-ray color of the ring sources, the overabundance of luminous sources in the combined XLF, and the flatter shape of the ring XLF.

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