First Application of the Fe XVII I(17.10 Å)/I(17.05 Å) Line Ratio to Constrain the Plasma Density of a Cosmic X-Ray Source
First Application of the Fe XVII I(17.10 Å)/I(17.05 Å) Line Ratio to Constrain the Plasma Density of a Cosmic X-Ray Source
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首次应用 Fe XVII I(17.10 Å)/I(17.05 Å) 线比来约束宇宙 X 射线源的等离子体密度
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发表时间：
2001
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通讯作者：
K. Fournier
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作者：
C. Mauche;D. Liedahl;K. Fournier
我们发现，在钱德拉高能透射光栅（HETG）光谱中观测到的Fe XVII I（17.10 Å）/I（17.05 Å）线比明显小于在太阳或其他晚型恒星上观测到的线比。利用基于HULLAC原子数据计算高电荷离子光谱模型的Livermore x射线光谱合成器，我们发现如果等离子体密度为ne≤3 × 1014 cm-3，则可以解释观测到的I（17.10 Å）/I（17.05 Å）线比。然而，如果能级-种群动力学中包含光激发，则只要光激发温度Tbb > 55 kK，线比可以解释为任何密度。白矮星表面热点的相对大小必须为f > 2%，才能使光激发在Fe - XVII能级-种群动力学中占主导地位。这个约束条件和观测到的x射线通量要求激波后流动的密度为n≤2 × 1014 cm-3。不管怎样，钱德拉的HETG光谱都要求等离子体密度比在太阳或其他晚型恒星上观察到的要大几个数量级。
We show that the Fe XVII I(17.10 Å)/I(17.05 Å) line ratio observed in the Chandra High-Energy Transmission Grating (HETG) spectrum of the intermediate polar EX Hya is significantly smaller than that observed in the Sun or other late-type stars. Using the Livermore X-Ray Spectral Synthesizer, which calculates spectral models of highly charged ions based on HULLAC atomic data, we find that the observed I(17.10 Å)/I(17.05 Å) line ratio can be explained if the plasma density ne ≳ 3 × 1014 cm-3. However, if photoexcitation is included in the level-population kinetics, the line ratio can be explained for any density if the photoexcitation temperature Tbb ≳ 55 kK. For photoexcitation to dominate the Fe XVII level-population kinetics, the relative size of the hot spot on the white dwarf surface must be f ≲ 2%. This constraint, and the observed X-ray flux, requires a density n ≳ 2 × 1014 cm-3 for the postshock flow. Either way, then, the Chandra HETG spectrum of EX Hya requires a plasma density that is orders of magnitude greater than that observed in the Sun or other late-type stars.