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arXiv 0903.2257astro-ph.GAastro-ph.CO
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活动星系中中等质量黑洞的X射线性质II。X射线--明亮的吸积现象和瘦骨嶙峋的可能证据

X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks

Louis-Benoit Desroches, Jenny E. Greene, Luis C. Ho

摘要:

利用Chandra X射线天文台的观测数据,研究了活动星系中光学选择的中等质量黑洞(~10^5- 10^6 M_Sun)的X射线性质.我们的观察是Greene & Ho(2007)的一项试点研究的延续。在观测到的8个天体中,有5个天体的X射线亮度在L_0.5-2 keV = 10^41- 10^43 erg s^-1范围内,与之前观测到的样本一致。具有足够计数以提取光谱的物体很好地符合吸收幂律。我们继续发现软光子指数1 < Γ_s < 2.7,其中N(E)\propto E^-Γ_s,与以前的活动星系核研究一致,但一般比其他窄线Seyfert 1活动核(NLS 1)平坦。软光子指数与X射线亮度和爱丁顿比密切相关,但不依赖于BH质量。没有理由包括任何额外的组件,如软过剩,虽然这可能是一个功能的相对效率较低的检测计数超过2千电子伏在这些相对较浅的观察。总体而言,X射线-光学光谱斜率α_ox比更大质量的系统,甚至其他NLS 1更平坦。只有X射线选择的具有非常高的爱丁顿比的NLS 1具有类似的α_ox。这表明在低质量和非常高的吸积率下,吸积结构发生了物理变化,可能是由于细长盘的出现。虽然对这些中等质量黑洞的X射线响度的详细物理解释还不确定,但非常引人注目的是,根据光学性质选择的目标在其更宽的光谱能量分布中应该如此明显地偏移。

英文摘要:

We present X-ray properties of optically-selected intermediate-mass (~10^5--10^6 M_Sun) black holes (BHs) in active galaxies (AGNs), using data from the Chandra X-Ray Observatory. Our observations are a continuation of a pilot study by Greene & Ho (2007). Of the 8 objects observed, 5 are detected with X-ray luminosities in the range L_0.5-2 keV = 10^41--10^43 erg s^-1, consistent with the previously observed sample. Objects with enough counts to extract a spectrum are well fit by an absorbed power law. We continue to find a range of soft photon indices 1 < Γ_s < 2.7, where N(E) \propto E^-Γ_s, consistent with previous AGN studies, but generally flatter than other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index correlates strongly with X-ray luminosity and Eddington ratio, but does not depend on BH mass. There is no justification for the inclusion of any additional components, such as a soft excess, although this may be a function of the relative inefficiency of detecting counts above 2 keV in these relatively shallow observations. As a whole, the X-ray-to-optical spectral slope α_ox is flatter than in more massive systems, even other NLS1s. Only X-ray-selected NLS1s with very high Eddington ratios share a similar α_ox. This is suggestive of a physical change in the accretion structure at low masses and at very high accretion rates, possibly due to the onset of slim disks. Although the detailed physical explanation for the X-ray loudness of these intermediate-mass BHs is not certain, it is very striking that targets selected on the basis of optical properties should be so distinctly offset in their broader spectral energy distributions.

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