来自差异旋转中子星的磁驱动风和短伽马射线暴的X射线余辉
Magnetically driven winds from differentially rotating neutron stars and X-ray afterglows of short gamma-ray bursts
摘要：
除了是最有希望的引力波来源之一，合并中子星双星也代表了解释短伽马射线暴（SGRB）现象的主要方案。最近的观测揭示了一个大的SGRB子类，它们的X射线余辉具有大致恒定的亮度，持续$10\!-\!10^4$ s。这些特征通常被认为是由均匀旋转的磁化物体的磁自旋驱动的长寿命中央引擎的证据。我们提出了一个不同的方案，其中的中央引擎供电的X射线发射是一个差动旋转的超大质量中子星（HMNS），发射准各向同性和重子加载的风驱动的磁场，这是建立通过差动旋转。我们的模型是支持长期的，三维的，广义相对论，和理想的磁流体动力学模拟，表明这种各向同性的发射是一个非常强大的功能。对于一个给定的HMNS，一个准直组件的存在敏感地依赖于初始磁场的几何形状，而静态电磁光度仅取决于最初存储在系统中的磁能。我们表明，我们的模型是兼容的观察到的时间尺度和光度，并表示后者在一个简单的标度关系。
英文摘要：
Besides being among the most promising sources of gravitational waves, merging neutron star binaries also represent a leading scenario to explain the phenomenology of short gamma-ray bursts (SGRBs). Recent observations have revealed a large subclass of SGRBs with roughly constant luminosity in their X-ray afterglows, lasting $10\!-\!10^4$ s. These features are generally taken as evidence of a long-lived central engine powered by the magnetic spin-down of a uniformly rotating, magnetized object. We propose a different scenario in which the central engine powering the X-ray emission is a differentially rotating hypermassive neutron star (HMNS) that launches a quasi-isotropic and baryon-loaded wind driven by the magnetic field, which is built-up through differential rotation. Our model is supported by long-term, three-dimensional, general-relativistic, and ideal magnetohydrodynamic simulations, showing that this isotropic emission is a very robust feature. For a given HMNS, the presence of a collimated component depends sensitively on the initial magnetic field geometry, while the stationary electromagnetic luminosity depends only on the magnetic energy initially stored in the system. We show that our model is compatible with the observed timescales and luminosities and express the latter in terms of a simple scaling relation.
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