Distance Limits on the Bright X-Ray Emission Toward the Galactic Center: Evidence for a Very Hot Interstellar Medium in the Galactic X-Ray Bulge
Distance Limits on the Bright X-Ray Emission Toward the Galactic Center: Evidence for a Very Hot Interstellar Medium in the Galactic X-Ray Bulge
复制标题
向银河系中心发射明亮 X 射线的距离限制：银河系 X 射线核球中存在非常热的星际介质的证据
DOI：
10.1086/317768
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
J. May
中科院分区：
文献类型：
--
作者：
R. Almy;D. McCammon;S. Digel;L. Bronfman;J. May
在~和1.5 keV能量下对弥散X射线背景的观测表明，银河系中心周围有一个很大的增强辐射区域。这种X射线增强的起源尚不清楚，但最好的候选者是附近的Loop I超级气泡和银河系X射线凸起。为了区分这两种可能性，必须确定X射线发射材料沿着视线的距离尺度。在1 ~ 337°，B ~ 4°方向上的13个ROSAT PSPC点的镶嵌图显示了远距离分子云复合体投射的1.5keV和1.5keV波段的X射线阴影。对阴影的分析表明，在这个方向观测到的辐射中有很大一部分（45% ± 9%）来自于位于d ~ 2 kpc的云复合体之外。这个遥远的发射源的隐含表面亮度可以占银河系平面吸收槽以外的增强发射的70%。这一结果表明，Loop I气泡不是增强X射线辐射的主要来源，并表明存在一个明亮的X射线源，占据银河系的中心区域，其径向范围为~6 kpc，X射线光度为~1039 ergs-1。我们研究了一些简单的模型的发射区，并将它们与ROSAT全天空调查。发射的热起源意味着等离子体温度约为4 × 106 K，总热能在6-9 × 1055尔格范围内。
Observations of the diffuse X-ray background at energies ~ and 1.5 keV show a large region of enhanced emission around the Galactic center. The origin of this X-ray enhancement is not known, but the best candidates are the nearby Loop I superbubble and a Galactic X-ray bulge. To differentiate between these two possibilities, the distance scales to the X-ray-emitting material along the line of sight must be established. A mosaic of 13 ROSAT PSPC pointings in the direction of l ~ 337°, b ~ 4° reveals X-ray shadows in the and 1.5 keV bands cast by a distant molecular cloud complex. Analysis of the shadows indicates that a large fraction (45% ± 9%) of the observed emission in this direction originates beyond the cloud complex, located at d ~ 2 kpc. The implied surface brightness of this distant emission source can account for ~70% of the enhanced emission away from the absorption trough in the Galactic plane. This result indicates that the Loop I bubble cannot be the principal source of the enhanced X-ray emission, and suggests the existence of a bright X-ray source occupying the central region of the Galaxy, with a radial extent of ~6 kpc and an X-ray luminosity of ~1039 ergs s-1. We examine some simple models of the emission region and compare them to the ROSAT all-sky survey. A thermal origin for the emission implies a plasma temperature of ~4 × 106 K and a total thermal energy in the range of 6-9 × 1055 ergs.