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arXiv 1409.0747astro-ph.HE
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低光度X射线源和银河脊X射线辐射

Low-luminosity X-ray sources and the Galactic ridge X-ray emission

R. S. Warwick

摘要:

利用XMM-牛顿回转巡天,我们构造了一个低光度银河系X射线源的硬带选择样本。图中显示了两个源星群,即日冕活动恒星和双星(ASB)和激变变星(CV),X射线光度范围为10^(28-34)erg/s(2-10 keV)。我们推导了2-10 keV的X射线光度函数(XLF)和每个粒子群的体发射率。按当地恒星的质量密度换算,发现ASB和CV的质量密度分别为1.08 +/- 0.16 x 10^28 erg/s/M和2.5 +/- 0.6 x 10^27 erg/s/M,比之前的估计高出2倍。我们使用新的XLF预测银河平面上l = 28.5度的X射线源计数,并表明结果与当前的观测约束是一致的。微弱的、未分辨的ASB和CV的X射线发射可以解释银河脊X射线发射(GRXE)的相当大一部分。我们讨论了一个模型,其中大约80%的6-10千电子伏GRXE强度是以这种方式产生的,其余部分可归因于X射线散射的星际介质和/或年轻的银河系源人口。大部分归因于ASB的硬X射线发射很可能是在耀斑发作期间产生的。

英文摘要:

Using the XMM-Newton Slew Survey, we construct a hard-band selected sample of low-luminosity Galactic X-ray sources. Two source populations are represented, namely coronally-active stars and binaries (ASBs) and cataclysmic variables (CVs), with X-ray luminosities collectively spanning the range 10^(28-34) erg/s (2-10 keV). We derive the 2-10 keV X-ray luminosity function (XLF) and volume emissivity of each population. Scaled to the local stellar mass density, the latter is found to be 1.08 +/- 0.16 x 10^28 erg/s/M and 2.5 +/- 0.6 x 10^27 erg/s/M, for the ASBs and CVs respectively, which in total is a factor 2 higher than previous estimates. We employ the new XLFs to predict the X-ray source counts on the Galactic plane at l = 28.5 deg and show that the result is consistent with current observational constraints. The X-ray emission of faint, unresolved ASBs and CVs can account for a substantial fraction of the Galactic ridge X-ray emission (GRXE). We discuss a model in which roughly 80 per cent of the 6-10 keV GRXE intensity is produced in this way, with the remainder attributable to X-ray scattering in the interstellar medium and/or young Galactic source populations. Much of the hard X-ray emission attributed to the ASBs is likely to be produced during flaring episodes.

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