General Relativistic Radiation MHD Simulations of Supercritical Accretion onto a Magnetized Neutron Star: Modeling of Ultraluminous X-Ray Pulsars
General Relativistic Radiation MHD Simulations of Supercritical Accretion onto a Magnetized Neutron Star: Modeling of Ultraluminous X-Ray Pulsars
复制标题
DOI：
10.3847/2041-8213/aa8222
复制
发表时间：
2017-07
期刊：
影响因子：
--
通讯作者：
H. R. Takahashi;K. Ohsuga
中科院分区：
文献类型：
--
作者：
H. R. Takahashi;K. Ohsuga
通过进行2.5维广义相对论辐射磁流体动力学模拟，我们证明了一颗非旋转磁化中子星上的超临界吸积，其中恒星表面偶极子场的磁场强度为1010g。我们发现超临界吸积流由两部分组成：吸积柱和截短的吸积盘。超临界吸积盘出现在离中子星较远的地方，截断在约≃3 R*处（R* = 106 cm为中子星半径），偶极子磁场产生的磁压力与吸积盘的辐射压力达到平衡。圆盘在截断半径附近的角动量通过磁转矩通过偶极场有效地向内传递，诱导中子星的自旋上升。估计的自旋上升速率为~−10−11 s s−1，与最近对超亮x射线脉冲星的观测结果一致。在截断半径内，气体沿着偶极子场落在中子星上，导致在北半球和南半球形成吸积柱。柱的净吸积率和光亮度分别为≤66 led /c2和≤10 led，其中led为爱丁顿光度，c为光速。我们的模拟支持一个假设，即超亮x射线脉冲星是由磁化中子星的超临界吸积提供动力的。
By performing 2.5-dimensional general relativistic radiation magnetohydrodynamic simulations, we demonstrate supercritical accretion onto a non-rotating, magnetized neutron star, where the magnetic field strength of dipole fields is 1010 G on the star surface. We found the supercritical accretion flow consists of two parts: the accretion columns and the truncated accretion disk. The supercritical accretion disk, which appears far from the neutron star, is truncated at around ≃3 R* (R* = 106 cm is the neutron star radius), where the magnetic pressure via the dipole magnetic fields balances with the radiation pressure of the disks. The angular momentum of the disk around the truncation radius is effectively transported inward through magnetic torque by dipole fields, inducing the spin up of a neutron star. The evaluated spin-up rate, ∼−10−11 s s−1, is consistent with the recent observations of the ultraluminous X-ray pulsars. Within the truncation radius, the gas falls onto a neutron star along the dipole fields, which results in a formation of accretion columns onto the northern and southern hemispheres. The net accretion rate and the luminosity of the column are ≃66 LEdd/c2 and ≲10 LEdd, where LEdd is the Eddington luminosity and c is the light speed. Our simulations support a hypothesis whereby the ultraluminous X-ray pulsars are powered by the supercritical accretion onto the magnetized neutron stars.