发表机构
Friedrich-Alexander Universität Erlangen-Nürnberg; Max-Planck-Institut für Radioastronomie; Tel Aviv University（埃尔朗根-纽伦堡大学; 马克斯·普朗克射电天文研究所; 特拉维夫大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文研究磁化中子星在吸积柱高度超过磁层半径时的无激波超爱丁顿吸积，构建了完全亚声速的半解析解，并通过模拟验证，提出此类模式可解释非脉冲超亮X射线源。
AI 中文摘要
强磁场使得吸积中子星能够形成磁控漏斗流。在足够高的吸积率下，这种流动会变为辐射压支撑。在传统图像中，磁层流包含一个近乎自由落体的跨声速外区、一个辐射介导的激波和一个亚声速吸积柱。我们研究了柱高度预计会超过磁层半径的情形。在这种情况下，具有驻立激波的自洽跨声速解不再可能，整个磁层流保持亚声速。我们在低马赫数极限下构建了一个完全亚声速、辐射支撑的磁层流的半解析流体动力学解。磁场在无力近似下处理，而流动结构由质量守恒、能量守恒以及沿磁力线的动量方程决定。我们使用代码HACol进行一维时变模拟来检验该解。无激波解是高度平流的。其焓分布接近绝热极限，而能量密度通过吸积通道侧面的质量和热量泄漏来调节。大部分可观测功率预计由离开中子星表面上方磁层流的等离子体释放。由于可见性选择和盘风中的散射，此类系统应与超爱丁顿吸积盘和低脉冲分数相关联。我们提出，许多包含中子星的非脉冲超亮X射线源可能以这种无激波模式吸积。
英文摘要
Strong magnetic fields allow accreting neutron stars to form magnetically controlled funnel flows. At sufficiently high accretion rates, such flows become radiation-pressure-supported. In the conventional picture, the magnetospheric flow contains a nearly free-falling transonic outer region, a radiation-mediated shock, and a subsonic accretion column. We investigate the regime in which the height of the column is expected to exceed the magnetospheric radius. In this case a self-consistent transonic solution with a standing shock is no longer possible, and the entire magnetospheric flow remains subsonic. We construct a semi-analytical hydrodynamical solution for a fully subsonic, radiation-supported magnetospheric flow in the low-Mach-number limit. The magnetic field is treated in the force-free approximation, while the flow structure is determined by mass conservation, energy conservation, and the momentum equation along the field lines. We test the solution using one-dimensional time-dependent simulations with the code HACol. The shock-free solution is highly advective. Its enthalpy profile is close to the adiabatic limit, while the energy density is regulated by leakage of mass and heat through the sides of the accretion channel. Most of the observable power is expected to be released by plasma leaving the magnetospheric flow above the neutron-star surface. Such systems should be associated with super-Eddington accretion discs and low pulse fractions due to visibility selection and scattering in the disc wind. We suggest that many non-pulsating ultraluminous X-ray sources containing neutron stars may accrete in this shock-free regime.
Comments11 pages, 5 figures, submitted to A&A
