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arXiv 2001.05638astro-ph.HE
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Circinus~ X-1在极低X射线通量下X射线谱线发射的起源

The Origins of X-ray Line Emissions in Circinus~X-1 at Very Low X-ray Flux

N. S. Schulz, T. E. Kallman, S. Heinz, P. Sell, P. Jonker, W. N. Brandt

摘要:

对含有中子星的X射线瞬变的吸积条件和形态仍然知之甚少。Circinus X-1是一个神秘的案例,我们观察到X射线通量的变化覆盖了四个数量级。我们使用钱德拉X射线天文台上的高能透射光栅光谱仪,在X射线通量非常低的情况下,对Circinus X-1进行了多次观测。在1.8 $\times10^{-11}$ \ergcm的通量下,我们观察到单个1.6 keV黑体光谱。观测到的10 $^{35}$ \ergsec的连续发光度大约低了两个数量级,不能解释观测到的光电离发光度,这表明X射线源的结构要复杂得多,正如以前所建议的那样,它被部分或完全遮蔽了。这影响了吸积盘的大多数发射,包括以前观察到的吸积盘日冕线发射。相反,观察到的最强的光电离线蓝移约$\sim 400$ \kms \,我们认为,他们起源于电离风的B5 Ia supergaint同伴支持以前的身份。Cir X-1中的中子星非常年轻,应该有很高的磁场。在所观测的光度下,黑体的发射半径足够小,与吸积热点相关联,作为X射线发射区。小的发射半径则指向低于$10^{12}$ G的场强,这将与在高磁场下偶尔观察到的I型X射线爆发一致。我们讨论的背景下,是一个高质量的X射线二进制与一些可能的Be星X射线二进制性质的重点。

英文摘要:

Accretion conditions and morphologies of X-ray transients containing neutron stars are still poorly understood. Circinus X-1 is an enigmatic case where we observe X-ray flux changes covering four orders of magnitude. We observed Circinus X-1 several times at its very lowest X-ray flux using the high energy transmission grating spectrometer on board the Chandra X-ray Observatory. At a flux of 1.8$\times10^{-11}$ \ergcm we observed a single 1.6 keV blackbody spectrum. The observed continuum luminosity of 10$^{35}$ \ergsec is about two orders of magnitude too low to explain the observed photoionized luminosity suggesting a much more complex structure of the X-ray source which is partially or entirely obscured as had been previously suggested. This affects most emissions from the accretion disk including previously observed accretion disk coronal line emissions. Instead, the strongest observed photoionized lines are blueshifted by about $\sim 400$ \kms\ and we suggest that they originate in the ionized wind of a B5Ia supergaint companion supporting a previous identification. The neutron star in Cir X-1 is very young and should have a high magnetic field. At the observed luminosity the emission radius of the blackbody is small enough to be associated with the accretion hot spot as the X-ray emitting region. The small emission radius then points to a field strength below $10^{12}$ G which would be consistent with the observation of occasional type I X-ray bursts at high magnetic fields. We discuss Cir X-1 in the context of being a high-mass X-ray binary with some emphasis on a possible Be-star X-ray binary nature.

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