银河系中心反射星云的IXPE和eXTP偏振考古学展望
Prospects for IXPE and eXTP polarimetric archaeology of the reflection nebulae in the Galactic center
摘要：
银河系中心反射星云的X射线偏振特性告诉我们照明源的方向（通过偏振角）和云沿视线的位置（通过偏振度）。然而，探测到的偏振度预计会降低，因为云的偏振发射与渗透到银河系中心区域的非偏振漫射发射混合在一起。在实际观测中，由于点扩散函数和非偏振仪器背景导致的源的形态拖尾也有助于稀释偏振度。到目前为止，这些影响从未被包括在稀释的估计中。我们评估了MC 2，Bridge-B2，G0.11-0.11，Sgr B2，Sgr C1，Sgr C2和Sgr C3分子云预测的X射线偏振的可探测性，这些分子云具有现代X射线成像偏振仪，如成像X射线偏振探测器（IXPE）和增强型X射线定时和偏振任务（eXTP）。我们进行现实的模拟X射线偏振观测考虑（借助钱德拉地图和光谱）的空间，光谱和偏振特性的所有漫发射和背景成分在每个感兴趣的区域。我们发现，在4.0-8.0 keV波段，其中的分子云的发射突出的其他组件，偏振度的稀释，包括由于源的形态涂抹的贡献，范围在$\sim$ 19\%和$\sim$ 55\%之间。我们的结论是，对于文献中报道的一些距离值，G0.11-0.11，Sgr B2，Bridge-B2，Bridge-E，Sgr C1和Sgr C3的稀释偏振度可以在2 Ms长的IXPE观测中检测到。eXTP的增强能力可以允许检测这里考虑的所有目标的4.0-8.0 keV。
英文摘要：
The X-ray polarization properties of the reflection nebulae in the Galactic center inform us about the direction of the illuminating source (through the polarization angle) and the cloud position along the line of sight (through the polarization degree). However, the detected polarization degree is expected to be lowered because the polarized emission of the clouds is mixed with the unpolarized diffuse emission that permeates the Galactic center region. In a real observation, also the morphological smearing of the source due to the point spread function and the unpolarized instrumental background contribute in diluting the polarization degree. So far, these effects have never been included in the estimation of the dilution. We evaluate the detectability of the X-ray polarization predicted for the MC2, Bridge-B2, G0.11-0.11, Sgr B2, Sgr C1, Sgr C2, and Sgr C3 molecular clouds with modern X-ray imaging polarimeters such as the Imaging X-ray Polarimetry Explorer (IXPE) and the Enhanced X-ray Timing and Polarimetry mission (eXTP). We perform realistic simulations of X-ray polarimetric observations considering (with the aid of Chandra maps and spectra) the spatial, spectral, and polarization properties of all the diffuse emission and background components in each region of interest. We find that in the 4.0-8.0 keV band, where the emission of the molecular clouds outshines the other components, the dilution of the polarization degree, including the contribution due to the morphological smearing of the source, ranges between $\sim$19\% and $\sim$55\%. We conclude that for some distance values reported in the literature, the diluted polarization degree of G0.11-0.11, Sgr B2, Bridge-B2, Bridge-E, Sgr C1, and Sgr C3 may be detectable in a 2 Ms long IXPE observations. The enhanced capabilities of eXTP may allow detecting the 4.0-8.0 keV of all the targets considered here.
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