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arXiv 1303.6337astro-ph.HE
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快自旋中子星系统4U 1636-53的宽铁谱线

Broad iron line in the fast spinning neutron-star system 4U 1636-53

Andrea Sanna, Beike Hiemstra, Mariano Mendez, Diego Altamirano, Tomaso Belloni, Manuel Linares

摘要:

利用XMM-Newton和Rossi X射线定时探测器(RXTE)对中子星低质量X射线双星4U 1636-53进行了6次同步观测,分析了它们的X射线谱。观测涵盖了源的几个状态,因此推断出大范围的质量吸积率。这六个观测结果显示在6.5 keV左右的光谱中有一条宽的发射线,可能是由于铁。我们拟合这条线与一组现象学模型的相对论加宽线,加上一个模型,占相对论涂抹和电离反射的吸积盘。后一种模型包括来自中子星表面或边界层的入射辐射和负责这些系统中的高能辐射的日冕。从与反射模型的拟合中,我们发现在六次观测中的四次中,对反射光谱的主要贡献来自中子星表面或边界层,而在另外两次观测中,对反射光谱的主要贡献来自日冕。我们发现,这两个组件的相对贡献是不相关的源的状态。从现象学模型中,我们发现,更好地描述了一个对称的,虽然广泛的,配置文件的铁线。谱线的宽度不能仅仅用康普顿展宽来解释,因此我们研究了相对论展宽的情况。我们进一步发现,从光盘,边界层和日冕的直接发射一般演变的方式与标准吸积盘模型一致,光盘和边界层变得更热,光盘向内移动的源从硬到软的状态。然而,铁线似乎并没有遵循同样的趋势。

英文摘要:

We analysed the X-ray spectra of six observations, simultaneously taken with XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the neutron star low-mass X-ray binary 4U 1636-53. The observations cover several states of the source, and therefore a large range of inferred mass accretion rate. These six observations show a broad emission line in the spectrum at around 6.5 keV, likely due to iron. We fitted this line with a set of phenomenological models of a relativistically broadened line, plus a model that accounts for relativistically smeared and ionised reflection from the accretion disc. The latter model includes the incident emission from both the neutron-star surface or boundary layer and the corona that is responsible for the high-energy emission in these systems. From the fits with the reflection model we found that in four out of the six observations the main contribution to the reflected spectrum comes from the neutron-star surface or boundary layer, whereas in the other two observations the main contribution to the reflected spectrum comes from the corona. We found that the relative contribution of these two components is not correlated to the state of the source. From the phenomenological models we found that the iron line profile is better described by a symmetric, albeit broad, profile. The width of the line cannot be explained only by Compton broadening, and we therefore explored the case of relativistic broadening. We further found that the direct emission from the disc, boundary layer, and corona generally evolved in a manner consistent with the standard accretion disc model, with the disc and boundary layer becoming hotter and the disc moving inwards as the source changed from the hard in to the soft state. The iron line, however, did not appear to follow the same trend.

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