Evolution of Iron Kα Line Emission in the Black Hole Candidate GX 339–4
Evolution of Iron Kα Line Emission in the Black Hole Candidate GX 339–4
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候选黑洞 GX 339–4 中铁 Kα 线发射的演化
DOI：
10.1086/320634
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
W. Cui
中科院分区：
文献类型：
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作者：
Y. Feng;S. Zhang;X. Sun;P. Durouchoux;Wan Chen;W. Cui
GX 339-4在一段时间内（1999年）被罗西X射线定时探测器定期监测，当时它的X射线通量显着下降（在3-20 keV波段从4.2 × 10-10下降到7.6 × 10-12 ergs cm-2 s-1），因为源进入“关闭”状态。“我们的光谱分析显示，在所有观测的源的观测光谱中，都存在一条突出的铁Kα线。这条线显示了一个有趣的演化：当测量的通量大于5 × 10-11 ergs cm-2 s-1时，它的中心在~6.4 keV，但在较低通量时，它会移动到~6.7 keV。线的等效宽度似乎向较低通量显著增加，尽管它可能对校准不确定性敏感。虽然吸积盘中中性或轻度电离的铁原子的荧光发射也许可以解释6.4 keV线，就像经常被引用的黑洞候选者一样，但似乎很难用这种机制来理解6.7 keV线，因为吸积盘在较低的通量下应该是较少电离的（除非它的密度急剧变化）。另一方面，6.7千电子伏的线可能是由于在光学薄，高度电离的等离子体中的氢或氦样铁离子的复合级联。我们讨论的背景下提出的吸积模型的结果。
GX 339-4 was regularly monitored with the Rossi X-Ray Timing Explorer during a period (in 1999) when its X-ray flux decreased significantly (from 4.2 × 10-10 to 7.6 × 10-12 ergs cm-2 s-1 in the 3-20 keV band), as the source settled into the "off state." Our spectral analysis revealed the presence of a prominent iron Kα line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at ~6.4 keV when the measured flux is above 5 × 10-11 ergs cm-2 s-1 but is shifted to ~6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to a recombination cascade of hydrogen- or helium-like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.