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arXiv 2109.01023astro-ph.HE
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低质量X射线脉冲星4U 1822-371的光谱分析:高倾角系统中的反射分量

Spectral analysis of the low-mass X-ray pulsar 4U 1822-371: Reflection component in a high-inclination system

A. Anitra, T. Di Salvo, R. Iaria, L. Burderi, A. F. Gambino, S. M. Mazzola, A. Marino, A. Sanna, A. Riggio

摘要:

X射线源4U 1822-371是一颗食低质量X射线双星和X射线脉冲星,拥有一颗NS,在X射线波段显示出周期性的脉动。系统的倾斜角度是如此之高,原则上,应该很难观察到中心物体的直接热发射和光谱的反射分量,因为它们被吸积盘的外边缘所隐藏。假设源在爱丁顿极限处吸积,我们分析了非同时XMM-牛顿和NuSTAR观测,并研究了平均宽带光谱,目的是调查反射分量的存在。在像4U 1822-371这样的高倾斜源中,以前没有观察到这样的分量。我们使用两种不同的反射模型,反射线加Pexplanar和自洽模型RfxConv的源的光谱发射建模。在我们的分析中,除了与中性或轻度电离铁相关的两条线外,我们还发现了光谱中反射成分的重要证据。连续光谱很好地拟合饱和康普顿模型和热黑体组件在较低的温度下由吸积盘发出。我们更新了星历表,在文献报道的最近的星历表上增加了两个新的日食时间。在我们提出的方案中,源是在爱丁顿极限吸积与$10^{38}$ erg/s的内禀光度,而观测到的光度是两个数量级低。尽管高的倾斜度,我们发现,反射分量是必需的,以适应残差在Fe线的范围和硬过剩观察到的光谱。内圆盘半径的最佳拟合值仍然是不确定的,并且依赖于模型。因此,需要更多的观测来证实这些结果,这可以为这个神秘而奇特的来源提供重要信息。

英文摘要:

The X-ray source 4U 1822-371 is an eclipsing low-mass X-ray binary and X-ray pulsar, hosting a NS that shows periodic pulsations in the X-ray band. The inclination angle of the system is so high that in principle, it should be hard to observe both the direct thermal emission of the central object and the reflection component of the spectrum because they are hidden by the outer edge of the accretion disc. Assuming that the source accretes at the Eddington limit, we analysed non-simultaneous XMM-Newton and NuSTAR observations and studied the average broadband spectrum, with the aim to investigate the presence of a reflection component. No such component has been observed before in a high-inclination source such as 4U 1822-371. We modelled the spectral emission of the source using two different reflection models, Diskline plus Pexriv and the self-consistent model RfxConv. In our analysis, we find significant evidence of a reflection component in the spectrum, in addition to two lines associated with neutral or mildly ionised iron. The continuum spectrum is well fitted by a saturated Comptonisation model and a thermal black-body component emitted by the accretion disc at a lower temperature. We updated the ephemeris, adding two new eclipse times to the most recent ephemeris reported in literature. In our proposed scenario, the source is accreting at the Eddington limit with an intrinsic luminosity of $10^{38}$ erg/s, while the observed luminosity is two orders of magnitude lower. Despite the high inclination, we find that a reflection component is required to fit residuals at the Fe line range and the hard excess observed in the spectrum. The best-fit value of the inner disc radius is still uncertain and model dependent. More observations are therefore needed to confirm these results, which can give important information on this enigmatic and peculiar source.

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