A Study of QSO Evolution in the X-Ray Band with the Aid of Gravitational Lensing
A Study of QSO Evolution in the X-Ray Band with the Aid of Gravitational Lensing
复制标题
借助引力透镜研究X射线波段的QSO演化
DOI：
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发表时间：
2004
期刊：
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通讯作者：
G. Garmire
中科院分区：
文献类型：
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作者：
X. Dai;G. Chartas;M. Eracleous;G. Garmire
我们介绍了钱德拉X射线天文台和XMM-牛顿观测到的相对高红移（1.7<z<4）引力透镜射电宁静类星体的小型调查结果。透镜放大效应使我们能够寻找类星体光谱和通量变化特性的变化，红移超过三个数量级的内在X射线光度。它将类星体性质的研究扩展到了在观测到的0.4-8 keV波段中低至10^{-15} erg cm^{-2} s^{-1}几倍的无透镜X射线通量水平。我们发现引力透镜射电宁静类星体样品的X射线幂律光子指数和X射线光度之间可能存在相关性。X射线光谱斜率随着X射线光度的增加而变陡。当我们将我们的数据与其他z>1.5的射电宁静类星体的样本结合起来时，这种相关性仍然很重要，特别是在10^{43}-10 45. 5} erg s^{-1}之间的低光度范围内。这个结果是令人惊讶的，考虑到这样的相关性是没有发现的类星体与红移低于1.5。我们认为，这种相关性可以理解的背景下，从类星体吸积盘的X射线发射的热日冕模型，假设我们的样本中的类星体吸积非常接近其爱丁顿极限和观测到的光度范围是由黑洞质量的范围（这一假设是一致的半解析模型的类星体演化的最新预测）。我们的透镜类星体的相对高的红移样本的X射线可变性的上限是一致的，与已知的相关性之间的变化和光度观察到的塞弗特1 s时，这种相关性外推到我们的样本的较大的光度。
We present results from a mini-survey of relatively high redshift (1.7<z<4) gravitationally lensed radio-quiet quasars observed with the Chandra X-ray Observatory and with XMM-Newton. The lensing magnification effect allows us to search for changes in quasar spectroscopic and flux variability properties with redshift over three orders of magnitude in intrinsic X-ray luminosity. It extends the study of quasar properties to unlensed X-ray flux levels as low as a few times 10^{-15} erg cm^{-2} s^{-1} in the observed 0.4-8 keV band. We find a possible correlation between the X-ray powerlaw photon index and X-ray luminosity of the gravitationally lensed radio-quiet quasar sample. The X-ray spectral slope steepens as the X-ray luminosity increases. This correlation is still significant when we combine our data with other samples of radio-quiet quasars with z>1.5, especially in the low luminosity range between 10^{43}-10^{45.5} erg s^{-1}. This result is surprising considering that such a correlation is not found for quasars with redshifts below 1.5. We suggest that this correlation can be understood in the context of the hot-corona model for X-ray emission from quasar accretion disks, under the hypothesis that the quasars in our sample accrete very close to their Eddington limits and the observed luminosity range is set by the range of black hole masses (this hypothesis is consistent with recent predictions of semi-analytic models for quasar evolution). The upper limits of X-ray variability of our relatively high redshift sample of lensed quasars are consistent with the known correlation between variability and luminosity observed in Seyfert 1s when this correlation is extrapolated to the larger luminosities of our sample.