标题： 中子星核心在“弱耦合”状态下的磁热演化：解耦扩散对磁星安静期X射线亮度的影响 显示英文标题

标题： Magnetothermal evolution of neutron star cores in the `weak-coupling' regime: implications of ambipolar diffusion for the quiescent X-ray luminosity of magnetars

摘要： 一些磁星观测到的高静态X射线亮度通常归因于其超强磁场的衰减和演化。已经提出了几种耗散机制，每种机制在恒星的不同区域以不同的效率运行。在此背景下，由于其对磁场强度的强烈依赖性和将磁能转化为热能的能力，ambi极化扩散（即中子星核心带电粒子相对于中子的相对运动）被提出作为一种有前景的候选机制。我们进行了轴对称磁流体力学模拟，研究了在ambi极化扩散的影响下，由正常（非库珀配对）物质组成的中子星核心的长期磁场演化。核心被建模为一个由中子和带电粒子流体（质子和电子）组成的两流体系统，并与磁场耦合。模拟既在恒定温度下进行，也在可变温度下进行。在后一种情况下，采用了一种使磁场和热演化解耦的策略，使得在一系列初始磁场强度下都能有效地进行热建模。在恒温条件下，我们得到了预期的结果，即中子达到扩散平衡，洛伦兹力由带电粒子的化学势梯度平衡，磁场满足非线性Grad-Shafranov方程。当包括热演化时，磁场$B \gtrsim 5 \times 10^{15} \,\text{G}$可以平衡ambi极化加热和中微子冷却，从而延迟演化超过$\sim 10^{3} \,[B/(5 \times 10^{15}\,\text{G})]^{-6/5}$年。尽管表面亮度比被动冷却有所增强，但单靠ambi极化扩散所产生的热量还不足以完全解释磁星中观测到的持续X射线辐射。 显示英文摘要

摘要： The high quiescent X-ray luminosity observed in some magnetars is widely attributed to the decay and evolution of their ultra-strong magnetic fields. Several dissipation mechanisms have been proposed, each operating with different efficiencies depending on the region of the star. In this context, ambipolar diffusion, i.e., the relative motion of charged particles with respect to neutrons in the neutron star core, has been proposed as a promising candidate due to its strong dependence on magnetic field strength and its capacity to convert magnetic energy into heat. We perform axisymmetric magnetohydrodynamic simulations to study the long-term magnetic evolution of a NS core composed of normal (non-Cooper paired) matter under the influence of ambipolar diffusion. The core is modeled as a two-fluid system consisting of neutrons and a charged-particle fluid (protons and electrons), coupled to the magnetic field. Simulations are performed both at constant and variable temperatures. In the latter case, a strategy that decouples the magnetic and thermal evolution is employed, enabling efficient thermal modeling across a range of initial magnetic field strengths. At constant temperature, we obtained the expected result where neutrons reach diffusive equilibrium, the Lorentz force is balanced by chemical potential gradients of charged particles, and the magnetic field satisfies a non-linear Grad-Shafranov equation. When thermal evolution is included, fields $B \gtrsim 5 \times 10^{15} \,\text{G}$ can balance ambipolar heating and neutrino cooling, delaying the evolution over $\sim 10^{3} \,[B/(5 \times 10^{15}\,\text{G})]^{-6/5}$ yr. Although the surface luminosity is enhanced compared to passive cooling, the heating from ambipolar diffusion alone is insufficient to fully explain the persistent X-ray emission observed in magnetars.