Two sources of diffuse X-ray emission from the Galactic Centre
Two sources of diffuse X-ray emission from the Galactic Centre
复制标题
银河系中心的两个漫射 X 射线源
DOI：
10.1038/364040a0
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发表时间：
1993
期刊：
影响因子：
64.8
通讯作者：
M. Pavlinsky
中科院分区：
文献类型：
--
作者：
Markevitch;R. Sunyaev;M. Pavlinsky
迄今为止，银河系中心微弱的扩展x射线源缺乏合理的解释。从Ginga卫星上对这个大致椭圆形的源的测量显示，电离铁的辐射线为6.7 kev，这表明x射线起源于光学薄的等离子体。但是为了解释硬x射线光谱，这个等离子体需要非常热——事实上，太热了，以至于不能被银河系中心的引力势所限制。我们最近发现，在能量高于11kev时，发射区的形态发生了变化：源在星系平面上延伸，类似于该区域分子气体云的分布。在这里，我们报告了在8-11 keV能量范围内的发射光谱中检测到明显的吸收特征。这一结果与空间分布的变化相结合，表明高能辐射是由致密分子云对附近致密源的x射线散射产生的。由于在较低能量下没有看到类似的吸收特征，因此较软的x射线发射可能仍然可以理解为等离子体的热发射，但所需的温度不再是不合理的高。
THE weak extended X-ray source at the Galactic Centre has so far lacked a reasonable explanation. Measurements of this roughly elliptical source from the Ginga satellite revealed1 emission in the 6.7-keV line of ionized iron, indicating that the X-rays originate in an optically thin plasma. But to account for the hard X-ray spectrum, this plasma needs to be very hot — too hot, in fact, to be confined by the gravitational potential of the Galactic Centre2. We have recently shown3 that the morphology of the emitting region changes at energies above 11 keV: the source becomes extended in the galactic plane, resembling the distribution of the molecular gas clouds in this region. Here we report the detection of a pronounced absorption feature in the emission spectrum in the energy range 8–11 keV. This result, combined with the changing spatial distribution, suggests that the high-energy emissions arise from the scattering of X-rays from the nearby compact sources by the dense molecular clouds. As no comparable absorption feature is seen at lower energies, the softer X-ray emissions may still be understood in terms of thermal emission from a plasma, but the required temperature is no longer unreasonably high.