X-ray polarimetry and evolution of isolated neutron stars

偏振法是研究天体的一个重要途径，与它们的光谱学相辅相成。x射线偏振研究仍然很少，但这种情况即将改变。为x射线偏振测量而设计的带有新仪器的轨道x射线天文台计划在未来十年使用（IXPE， NASA; eXTP，中国）。它们将有助于研究相对热（色温数MK）磁化和潜在磁化中子星（NSs）。在这个项目中，我们计划通过观察到的x射线热辐射来研究几类孤立的（非吸积的）NSs （ins）的x射线辐射偏振特性：超新星残骸中的中心致密天体（CCOs）， x射线INSs （XINSs）和磁星。一些cco的光谱与均匀碳大气的光谱很好地拟合。然而，我们不能完全排除它们拥有热点的可能性，类似于其他显示脉动的cco。偏振测量可以区分均匀的碳和非均匀的氢或氦NS大气。澄清这一问题对于理解超新星演化和超新星内部超致密物质的物理特性是非常重要的。具有强磁场的磁星和XINSs的x射线极化研究对于解决磁场构型的几何简并以及理解高磁化NS表面的物理过程具有重要意义。以前的研究是使用纯氢模型大气或浓缩的NS表面模型进行的。我们建议将这些研究扩展到部分电离的氦大气，从理论的角度来看，这对磁星更有可能。强磁化的中子星具有高度不均匀的表面温度分布，除了光谱研究外，还可以通过极化研究更有信心地确定。INS温度分布是地壳和地核磁热演化的结果，受超致密物质物理特性的调控。因此，热惯性辐射的光谱和极化研究只有结合惯性辐射的磁热演化模型才能对超致密物质的物理特性提供约束。我们将模拟NS的磁和热演化，以建立自一致的模型，以可靠地解释NS x射线发射偏振测量的物理解释。本文将对几个热发射卫星进行新的光学偏振和x射线光谱观测，并对它们的x射线偏振数据进行模拟。

Polarimetry is an important channel of study of astronomical objects, complementary to their spectroscopy. X-ray polarization studies are still rare, but the situation is about to change. Orbital X-ray observatories with new instruments onboard, designed for X-ray polarization measurements, are planned for the next decade (IXPE, NASA; eXTP, China). They will be useful for studies of relatively hot (color temperatures of several MK) magnetized and potentially magnetized neutron stars (NSs). In this project, we plan to investigate the polarization properties of X-ray radiation of several classes of isolated (non-accreting) NSs (INSs) with observed X-ray thermal emission: central compact objects (CCOs) in supernova remnants, X-ray INSs (XINSs), and magnetars. Spectra of some CCOs are well fitted by the spectra of uniform carbon atmospheres. However, one cannot completely exclude the possibility that they possess hot spots, similar to the other CCOs that show pulsations. Polarization measurements can distinguish between uniform carbon and non-uniform hydrogen or helium NS atmospheres. Clarification of this issue is important for understanding NS evolution and the physics of superdense matter inside the NSs. X-ray polarization studies of magnetars and XINSs, which possess strong magnetic fields, are important for resolving geometrical degeneracy of the magnetic field configuration, and for understanding of the physical processes at the highly magnetized NS surface. Previous investigations were performed using pure hydrogen model atmospheres or condensed NS surface models. We suggest to extend these investigations to partially ionized helium atmospheres, which are more plausible for magnetars from theoretical point of view. Strongly magnetized neutron stars have highly non-uniform surface temperature distributions, which can be more confidently determined using polarimetric studies in addition to spectroscopic ones. The INS temperature distribution results from magneto-thermal evolution of the NS crust and core, which is regulated by the physics of superdense matter. Therefore, spectroscopic and polarimetric studies of thermal INS radiation can provide constraints on the physics of superdense matter only in combination with models of the magneto-thermal evolution of the NSs. We will simulate NS magnetic and thermal evolution to construct self-consistent models for reliable physical interpretation of the polarization measurements of X-ray emission of the INSs. New optical polarization and X-ray spectral observations of several thermally emitting INSs, as well as simulations of X-ray polarization data for them will be performed.