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arXiv 1712.09024astro-ph.HE
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用朱雀发现6.4 keV线和G323 .7 $-$ 1.0的软X射线发射

Discovery of 6.4 keV line and soft X-ray emissions from G323.7$-$1.0 with Suzaku

Shigetaka Saji, Hironori Matsumoto, Masayoshi Nobukawa, Kumiko K. Nobukaw, Hideki Uchiyama, Shigeo Yamauchi, Katsuji Koyama

摘要:

利用$-$ 1.0对银河系超新星遗迹(SNR)候选者G323.7的朱雀X射线数据进行分析,寻找X射线辐射。在6.4 keV线和软X射线中的空间扩展增强被发现在无线电外壳内部或上。软X射线增强将是沿射电壳层的壳状X射线发射中最热的部分。在$4.1 σ$的显著性水平下检测到6.4 keV谱线增强。等效宽度(EW)的下限为1.2 keV。6.4 keV谱线的能量质心是$6.40 \pm 0.04$ keV,表明铁的电离程度低于类氖态。如果6.4千电子伏的线起源于电离非平衡热等离子体,富铁的喷出物在低电离状态的存在是必需的,这是不利的相对老的年龄的SNR。6.4 keV的谱线增强可能是由于高能粒子在致密星际介质中对铁原子的K壳层电离所致。由于没有辐照的X射线源,6.4 keV谱线增强的起源不太可能是光电离。大EW只能用能量为$\sim 10$ MeV的宇宙射线质子引起的K壳层电离来解释,这可能是由G323.7 $-$ 1.0中的激波加速产生的。

英文摘要:

In this paper, the Suzaku X-ray data of the Galactic Supernova Remnant (SNR) candidate G323.7$-$1.0 are analyzed to search for X-ray emission. Spatially-extended enhancements in the 6.4 keV line and in soft X-rays are found inside or on the radio shell. The soft X-ray enhancement would be the hottest part of the shell-like X-ray emission along the radio shell. The 6.4 keV line enhancement is detected at a significance level of $4.1 σ$. The lower limit of the equivalent width (EW) is 1.2 keV. The energy centroid of the 6.4 keV line is $6.40 \pm 0.04$ keV, indicating that the iron is less ionized than the Ne-like state. If the 6.4 keV line originates from ionizing non-equilibrium thermal plasma, presence of iron-rich ejecta in a low-ionization state is required, which is disfavored by the relatively old age of the SNR. The 6.4 keV line enhancement would be due to K-shell ionization of iron atoms in a dense interstellar medium by high-energy particles. Since there is no irradiating X-ray source, the origin of the 6.4 keV line enhancement is not likely the photoionization. The large EW can only be explained by K-shell ionization due to cosmic-ray protons with an energy of $\sim 10$ MeV, which might be generated by the shock acceleration in G323.7$-$1.0.

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