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arXiv 1703.07005astro-ph.HE
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磁化中子星的超爱丁顿吸积

Super-Eddington accretion onto a magnetized neutron star

Anna Chashkina, Pavel Abolmasov, Juri Poutanen

摘要:

大多数超亮X射线源被认为是在爱丁顿极限以上吸积的物体。在最近发现的超亮X射线双星中,吸积星是一颗中子星,因此质量很小,爱丁顿极限也很小。这种天体周围的吸积盘结构会影响重要的观测量,如平衡周期、周期导数和磁层的大小。我们提出了一个模型,一个接近标准的吸积盘与磁层相互作用,只有在一个薄层附近的内盘边缘。我们的计算表明,磁层的大小可以表示为经典的阿尔文半径乘以无量纲因子$ξ$,它只取决于磁盘的厚度。在辐射压主导的盘的情况下,磁层的大小不依赖于质量吸积率。一般来说,增加圆盘厚度会导致以阿尔文半径为单位的更大磁层尺寸。对于足够大的质量吸积率和磁矩,不仅要考虑盘内的磁场压力和辐射压力,还要考虑吸积柱中靠近中子星表面产生的辐射压力。磁层的大小可能会增加多达两倍的影响,有关的磁盘厚度和辐射的中心源的结果。考虑到这些影响,对中子星磁矩的估计值降低了好几倍。

英文摘要:

Most of ultraluminous X-ray sources are thought to be objects accreting above their Eddington limits. In the recently identified class of ultraluminous X-ray pulsars, accretor is a neutron star and thus has a fairly small mass with a small Eddington limit. The accretion disc structure around such an object affects important observables such as equilibrium period, period derivative and the size of the magnetosphere. We propose a model of a nearly-standard accretion disc interacting with the magnetosphere only in a thin layer near the inner disc rim. Our calculations show that the size of the magnetosphere may be represented as the classical Alfvén radius times a dimensionless factor $ξ$ which depends on the disc thickness only. In the case of radiation-pressure-dominated disc, the size of the magnetosphere does not depend on the mass accretion rate. In general, increasing the disc thickness leads to a larger magnetosphere size in units of the Alfvén radius. For large enough mass accretion rates and magnetic moments, it is important to take into account not only the pressure of the magnetic field and the radiation pressure inside the disc, but also the pressure of the radiation produced close to the surface of the neutron star in accretion column. The magnetospheric size may increase by up to factor of two as a result of the effects related to the disc thickness and the irradiation from the central source. Accounting for these effects reduces the estimate of the neutron star magnetic moment by a factor of several.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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