We study the mutual influence of thermal and magnetic evolution in a neutron star's crust in axial symmetry. Taking into account realistic microphysical inputs, we find the heat released by Joule effect consistent with the circulation of currents in the crust, and we incorporate its effects in 2D cooling calculations. We solve the induction equation numerically using a hybrid method (spectral in angles, but a finite--differences scheme in the radial direction), coupled to the thermal diffusion equation. We present the first long term 2D simulations of the coupled magneto-thermal evolution of neutron stars. This substantially improves previous works in which a very crude approximation in at least one of the parts (thermal or magnetic diffusion) has been adopted. Our results show that the feedback between Joule heating and magnetic diffusion is strong, resulting in a faster dissipation of the stronger fields during the first million years of a NS's life. As a consequence, all neutron stars born with fields larger than a critical value (about 5 10^13 G) reach similar field strengths (approximately 2-3 10^{13} G) at late times. Irrespectively of the initial magnetic field strength, after $10^6$ years the temperature becomes so low that the magnetic diffusion timescale becomes longer than the typical ages of radio--pulsars, thus resulting in apparently no dissipation of the field in old NS. We also confirm the strong correlation between the magnetic field and the surface temperature of relatively young NSs discussed in preliminary works. The effective temperature of models with strong internal toroidal components are systematically higher than those of models with purely poloidal fields, due to the additional energy reservoir stored in the toroidal field that is gradually released as the field dissipates.
Magnetohydrodynamic Simulations of Accretion Disks around a Weakly Magnetized Neutron Star in Strong Gravity
我们对弱磁化中子星周围的吸积盘进行了二维高分辨率磁流体动力学（MHD）模拟。利用Paczenski，B.，P. J. Witta（1980年）。当磁环连接中子星和吸积盘时，来自吸积盘或旋转的中子星的扭曲注入触发了磁环的膨胀。由于膨胀的磁环阻止了流向中子星的磁极的物质流入，盘状物质就聚集在磁层和盘状物质的边界上。在磁环中发生的磁重联创造了一个通道，盘物质可以沿着这个通道吸积并卸载磁层。这个过程产生准周期性变化的吸积流在最里面的区域的磁盘。我们发现了两种振荡。一种是由磁重联调节的磁层振荡。另一种是径向圆盘振荡。振荡的典型频率为100 Hz至2 kHz。此外，我们预测QPO源不可避免地伴随着X射线耀斑的磁重联和双极流出的热X射线发射等离子体类似的光学喷流在原恒星。
B-field Determination from Magnetoacoustic Oscillations in kHz QPO Neutron Star Binaries: Theory and Observations
我们提出了一种基于观察到的kHz和粘性QPO频率以及康普顿化模型的最佳拟合光学深度和温度来确定中子星周围B场的方法。在过渡层QPO模型的框架下，我们分析了在中子星表面和开普勒盘内缘之间的层中磁声波的形成。我们推导出不同径向过渡层振荡状态下磁声波频率的公式。我们证明了我们的模型可以使用QPO作为一种新的探针来确定QPO发生区域中4U 1728-42、GX 340+0和Sco X-1的磁场强度。观测结果表明，粘性频率对开普勒频率的依赖性与磁声波频率对偶极子磁场的开普勒频率的推断依赖性密切相关。磁声波的依赖性是基于一个单一的参数，磁矩的恒星估计从磁场强度在过渡层。对于所有研究的源，最适合的磁矩参数约为（0.5-1）x 10^{25} G cm ^3。从观测数据来看，在距离中子星20 km以内的范围内，三个源的磁场都被强烈地约束为中子星表面上强度为10^{7-8} G的偶极场。
The impact of magnetic field on the thermal evolution of neutron stars
研究了B> 10 e 13 G的强磁场对中子星热演化的影响，包括磁场衰变引起的地壳加热。为此，我们进行了二维冷却模拟与各向异性的热导率考虑所有相关的中微子发射过程的现实中子星。中子星的标准冷却模型受到质疑，显示磁场有相关的（在许多情况下占主导地位的）热演化的影响。磁场的存在显着影响的热表面分布和冷却的历史，这些对象期间，早期中微子冷却时代和后期光子冷却时代。因此，最小冷却方案比通常假设的更复杂。磁化中子星的一致的磁热演化需要解释观测结果。
