High Forbidden-to-resonance Line Ratio of O vii Discovered from the Cygnus Loop
High Forbidden-to-resonance Line Ratio of O vii Discovered from the Cygnus Loop
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DOI：
10.3847/1538-4357/aaf8a6
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发表时间：
2018-12
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影响因子：
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通讯作者：
H. Uchida;S. Katsuda;H. Tsunemi;K. Mori;L. Gu;R. Cumbee;R. Petre;T. Tanaka
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作者：
H. Uchida;S. Katsuda;H. Tsunemi;K. Mori;L. Gu;R. Cumbee;R. Petre;T. Tanaka
电荷交换（CX）是激波物理学中的一个重要过程，因为它表明下游离子与周围中性氢之间的相互作用，表明存在无碰撞激波。我们提出了一个高分辨率的光谱学的X射线亮点在附近的超新星遗迹（SNR），天鹅座圈，与反射光栅光谱仪（RGS）上的XMM-牛顿。目标是一个紧凑的多节结构，称为“西南结”（SW-K），位于外壳的外缘，爆炸波可能与周围致密的物质相互作用。SW-K的RGS谱显示了低于101 keV的谱线特征的细节，在那里我们发现了O vii Heα的高禁共振谱线比。软带（10-35 μ m）光谱很好地解释了一个热分量与CX X射线发射被中性和电离吸收剂掩盖。CX X射线发射的存在将为SNR的冲击物理学提供新的见解。高分辨率光谱还显示，CNO，Ne和Fe丰度确实低于太阳值（0.2-0.4太阳）在SW-K区域。我们的结果提供了一个线索，以解决以前已知的“低丰度问题”报告从一些进化的信噪比。
Charge exchange (CX) is an important process in shock physics because it indicates an interaction between downstream ions and ambient neutral hydrogen, suggesting the presence of a collisionless shock. We present a high-resolution spectroscopy of an X-ray bright spot in a nearby supernova remnant (SNR), the Cygnus Loop, with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The target is a compact knotty structure called the “southwestern knot” (SW-K) located at the outer edge of the shell, where the blast wave is likely interacting with dense surrounding materials. The RGS spectrum of the SW-K shows details of the line features below ∼1 keV, where we discover a high forbidden-to-resonance line ratio of O vii Heα. The soft-band (10–35 Å) spectrum is well explained by a thermal component with a CX X-ray emission obscured by neutral and ionized absorbers. The presence of the CX X-ray emission will provide new insights into the shock physics of SNRs. The high-resolution spectroscopy also reveals that the CNO, Ne, and Fe abundances are truly lower than the solar values (0.2–0.4 solar) at the SW-K region. Our result gives a clue to solving the previously known “low-abundance problem” reported from a number of evolved SNRs.