AI 中文总结
研究X射线脉冲星亚临界吸积时磁层流的热平衡，考虑多种加热冷却过程，计算温度剖面，发现低光度时吸积等离子体不再完全电离，磁层吸积通过部分电离介质进行，有别于传统认知。
AI 中文摘要
X射线脉冲星中的磁层吸积流塑造了其光谱、偏振和变异性。我们对亚临界状态（$L \lesssim 10^{37}\,\mathrm{erg\,s^{-1}}$）下环绕中子星磁层的流的热平衡进行建模，此时辐射力不控制动力学且单康普顿散射占主导。能量收支包括表面X射线的康普顿加热、汇聚流中的压缩（绝热）加热以及以自由自由发射为主且还有回旋发射贡献的辐射冷却。我们表明这些过程的相互作用导致内磁层流的有效冷却。计算了流温度剖面与光度的函数关系，发现在恒星表面附近，当$L < 10^{35}\,\mathrm{erg\,s^{-1}}$时温度可降至几十电子伏特。在此条件下，此处建模为纯氢的吸积等离子体不再完全电离。在X射线脉冲星典型的强磁场中，这样的温度允许电子和质子部分复合成中性氢。结果，很大一部分流变得弱电离，而外部光照仅在中子星表面上方几何上很薄的一层内部分电离这种气体。这意味着低光度下的磁层吸积通过部分电离介质进行，这与通常假设的完全电离流不同。
英文摘要
Magnetospheric accretion flows in X-ray pulsars shape their spectra, polarization, and variability. We model the thermal balance of the flow enveloping the neutron star magnetosphere in the sub-critical regime ($L \lesssim 10^{37}\,\mathrm{erg\,s^{-1}}$), where radiation forces do not control the dynamics and single Compton scatterings dominate. The energy budget includes Compton heating by surface X-rays, compressional (adiabatic) heating in the converging flow, and radiative cooling dominated by free-free emission and contributed also by cyclotron emission. We show that the interplay of these processes leads to efficient cooling of the flow in the inner magnetosphere. We compute the flow temperature profile as a function of luminosity and find that near the stellar surface the temperature can fall to a few tens of eV at $L < 10^{35}\,\mathrm{erg\,s^{-1}}$. Under such conditions, the accreting plasma, modelled here as pure hydrogen, is no longer fully ionized. In the strong magnetic fields typical for X-ray pulsars, such temperatures permit partial recombination of electrons and protons into neutral hydrogen. As a result, a significant fraction of the flow becomes weakly ionized, while external illumination ionizes this gas only partially within a geometrically thin layer immediately above the neutron star surface. This implies that magnetospheric accretion at low luminosities proceeds through a partially ionized medium, in contrast to the commonly assumed fully ionized flow.
Commentsaccepted for publication in MNRAS, 19 pages, 9 figures
