弱X射线源通量和吸收的估算方法
Methods for Estimating Fluxes and Absorptions of Faint X-ray Sources
摘要：
计数很少的X射线源可以用低噪声X射线探测器识别，如钱德拉X射线天文台上的ACIS。这些源通常太微弱，无法使用完善的方法（如XSPEC拟合）进行参数光谱建模。本文讨论了用非参数方法估算沿瞄准线的气体对这些源的表观和本征宽带X射线通量和软X射线吸收。表观通量是由源计数率与仪器有效面积之比在所选波段上取平均值来估算的。吸收，内在的通量，这些量的误差估计从源光度的数量与那些高S/N光谱，模拟使用光谱模型特性的研究中的天体物理源的类的比较。这种方法的概念类似于光学和红外天文学中长期使用的颜色星等图，用X射线中值能量代替颜色指数，用X射线源计数代替星等。我们的非参数方法进行了测试对2000暗弱源的视光谱在钱德拉观测丰富的年轻星团在M17 HII区。我们表明，固有的X射线属性可以确定小的偏差和合理的精度，使用这些可观察到的光度量，而不采用非线性参数光谱建模的不确定性和耗时的方法。我们的方法是校准的热谱特征的年轻恒星星团，但重新校准应该是可能的一些其他类别的微弱X射线源，如河外活动星系核。
英文摘要：
X-ray sources with very few counts can be identified with low-noise X-ray detectors such as ACIS onboard the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broad-band X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high S/N spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M17 HII region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of non-linear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic AGN.
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