威尔曼1：与钱德拉在黑暗中拍摄的X射线
Willman 1: An X-ray shot in the dark with Chandra
摘要：
无菌中微子是一种弱相互作用粒子，出现在标准粒子物理学的某些扩展框架中，自然符合暖暗物质候选粒子的性质。我们提出了一个深入的档案钱德拉观测威尔曼1，一个最黑暗的传说中的超微弱的矮星系，不包括在1.6-16千电子伏的质量范围内的55个pc的观察范围内的不育中微子的存在的分析。对钱德拉数据的光谱分析未能发现任何可能与暗物质粒子的辐射衰变有关的非仪器光谱特征。因此，我们建立上界的不育中微子参数空间，并讨论它的背景下，以前的测量。关于点源总体，我们在中心5弧分内识别出总共26个源，其极限0.5-2.0 keV X射线通量为6 x 10^{-16} erg cm^{-2} s^{-1}。虽然这些来源中的一些可能是威尔曼1的正式成员，但我们没有发现任何突出的证据来证明明亮的X射线源的不寻常人口或人口稠密的集群核心。事实上，整个X射线族群可以用背景活动星系核和/或与威尔曼1号无关的前景恒星来解释。最后，讨论了SDSS DR 7星表中的X射线点状星群与光源的可能联系。
英文摘要：
The sterile neutrino is a weakly-interacting particle that emerges in the framework of certain extensions of standard particle physics and that fits naturally with the properties of a warm dark matter particle candidate. We present an analysis of a deep archival Chandra observation of Willman 1, one of the darkest purported ultra-faint dwarf galaxies, that excludes the presence of sterile neutrinos in the 1.6-16 keV mass range within 55 pc of its centre down to the limits of the observation. Spectral analysis of the Chandra data fails to find any non-instrumental spectral feature possibly connected with the radiative decay of a dark matter particle. Accordingly, we establish upper bounds on the sterile neutrino parameter space and discuss it in the context of previous measurements. Regarding the point source population, we identify a total of 26 sources within the central 5 arcminutes to a limiting 0.5-2.0 keV X-ray flux of 6 x 10^{-16} erg cm^{-2} s^{-1}. While some of these sources could be formal members of Willman 1, we find no outstanding evidence for either an unusual population of bright X-ray sources or a densely populated cluster core. In fact, the entire X-ray population could be explained by background active galactic nuclei and/or foreground stars unrelated to Willman 1. Finally, possible associations of the X-ray point like population with optical sources from the SDSS DR7 catalogue are discussed.
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