银河系X射线吸收的刻度
Calibration of X-ray absorption in our Galaxy
摘要：
预测软X射线吸收沿视线通过我们的银河系是至关重要的了解河外源的光谱，但需要一个很好的估计前景柱密度的光电吸收物种。假设均匀的元素丰度，这简化为具有总氢柱密度的良好估计，N（Htot）=N（H1）+2N（H2）。使用映射的21厘米无线电发射可靠地提供了原子分量N（H1），但是估计分子氢柱密度N（H2），预期对于任何特定方向是困难的。伽玛射线暴的X射线余辉是探测银河系中X射线吸收的理想光源，因为它们是河外的，数量众多，明亮，光谱简单，随机出现在整个天空中。我们描述了一个经验的方法，利用493余辉探测的雨燕XRT，确定N（Htot）通过银河系，它提供了一个改进的估计在我们的银河系的X射线吸收，从而导致更可靠的测量的固有X射线吸收，并可能，其他光谱参数，河外X射线源。我们得到一个简单的函数，依赖于产品的原子氢柱密度，N（HI），和尘埃消光，E（B-V），它描述的变化的分子氢柱密度，N（H2），我们的银河系，在天空中。使用由此产生的N（Htot），我们表明，尘埃与氢的比例与一氧化碳排放量，并使用这个比例来估计形成星际尘埃颗粒的材料的比例。与以前的标准方法相比，我们得到的配方代表了银河系吸收的重大修订，特别是在银河系低纬度地区。
英文摘要：
Prediction of the soft X-ray absorption along lines of sight through our Galaxy is crucial for understanding the spectra of extragalactic sources, but requires a good estimate of the foreground column density of photoelectric absorbing species. Assuming uniform elemental abundances this reduces to having a good estimate of the total hydrogen column density, N(Htot)=N(HI)+2N(H2). The atomic component, N(HI), is reliably provided using the mapped 21 cm radio emission but estimating the molecular hydrogen column density, N(H2), expected for any particular direction, is difficult. The X-ray afterglows of GRBs are ideal sources to probe X-ray absorption in our Galaxy because they are extragalactic, numerous, bright, have simple spectra and occur randomly across the entire sky. We describe an empirical method, utilizing 493 afterglows detected by the Swift XRT, to determine N(Htot) through the Milky Way which provides an improved estimate of the X-ray absorption in our Galaxy and thereby leads to more reliable measurements of the intrinsic X-ray absorption and, potentially, other spectral parameters, for extragalactic X-ray sources. We derive a simple function, dependent on the product of the atomic hydrogen column density, N(HI), and dust extinction, E(B-V), which describes the variation of the molecular hydrogen column density, N(H2), of our Galaxy, over the sky. Using the resulting N(Htot) we show that the dust-to-hydrogen ratio is correlated with the carbon monoxide emission and use this ratio to estimate the fraction of material which forms interstellar dust grains. Our resulting recipe represents a significant revision in Galactic absorption compared to previous standard methods, particularly at low Galactic latitudes.
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