Multiple Components of the Luminous Compact X-Ray Source at the Edge of Holmberg II Observed by ASCA and ROSAT
Multiple Components of the Luminous Compact X-Ray Source at the Edge of Holmberg II Observed by ASCA and ROSAT
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DOI：
10.1086/321087
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发表时间：
2001-02
期刊：
影响因子：
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通讯作者：
T. Miyaji;I. Lehmann;G. Hasinger
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文献类型：
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作者：
T. Miyaji;I. Lehmann;G. Hasinger
我们报告了对新的 ASCA 观测结果和在 M81 群中附近的恒星形成矮星系 Holmberg II (UGC 4305) 边缘发现的致密发光 X 射线源的档案 ROSAT 数据的分析结果。我们在该源的 X 射线特性中发现了许多新特征。我们的新 ASCA 光谱显示，X 射线发射延伸到硬带，并且可以通过光子光谱指数 ∼ 1.9 的幂律来最好地描述，而具有低丰度 (∼0.2 Z⊙) 的 kT ∼ 5 keV 热等离子体也是可以接受的。与一些具有相似光度的离核 X 射线源不同，ASCA 光谱不适合多色圆盘黑体。 ASCA-ROSAT 联合谱表明该谱有两个组成部分：硬幂律分量和温热等离子体 (kT ∼ 0.3 keV)。需要比我们银河系额外的吸收。 ROSAT HRI 图像的摆动校正清楚地揭示了占总 X 射线发射的 27% ± 5% 的扩展分量的存在。这些观察结果表明 X 射线发射中有不止一种成分。点状成分的特性表明，除非发生射束，否则会吸积到中等质量黑洞上。我们认为扩展分量并非来自中心辐射的散射光学厚云的电子散射和/或反射。对这个X射线源的可能解释包括多个超新星遗迹为中等质量黑洞提供能量。
We report the results of the analysis of new ASCA observations and archival ROSAT data of the compact luminous X-ray source found at the edge of the nearby star-forming dwarf galaxy Holmberg II (UGC 4305) in the M81 group. We have found a number of new features in the X-ray properties of this source. Our new ASCA spectrum revealed that the X-ray emission extends to the hard band and can be best described by a power law with a photon spectral index Γ ∼ 1.9, while a kT ∼ 5 keV thermal plasma with a low abundance (∼0.2 Z⊙) is also acceptable. The ASCA spectrum does not fit with a multicolor disk blackbody, unlike some off-nucleus X-ray sources with similar luminosities. The joint ASCA-ROSAT spectrum suggests two components to the spectrum: the hard power-law component and a warm thermal plasma (kT ∼ 0.3 keV). An additional absorption over that of our galaxy is required. The wobble correction of the ROSAT HRI image has clearly unveiled the existence of an extended component that amounts to 27% ± 5% of the total X-ray emission. These observations indicate that there are more than one component in the X-ray emission. The properties of the pointlike component indicate an accretion onto an intermediate-mass black hole unless a beaming is taking place. We argue that the extended component does not come from electron scattering and/or reflection by scattered optically thick clouds of the central radiation. Possible explanations of this X-ray source include multiple supernova remnants feeding an intermediate-mass black hole.