Structures of X-ray emitting magnetic polar regions on neutron stars in X-ray pulsars are studied in a range of the accretion rate, 10$^{17}$ g s$^{-1} \sim 10^{18}$ g s$^{-1}$. It is shown that a thin but tall, radiation energy dominated, X-ray emitting polar cone appears at each of the polar regions. The height of the polar cone is several times as large as the neutron star radius. The energy gain due to the gravity of the neutron star in the polar cone exceeds the energy loss due to photon diffusion in the azimuthal direction of the cone, and a significant amount of energy is advected to the neutron star surface. Then, the radiation energy carried with the flow should become so large for the radiation pressure to overcome the magnetic pressure at the bottom of the cone. As a result, the matter should expand in the tangential direction along the neutron star surface, dragging the magnetic lines of force, and form a mound-like structure. The advected energy to the bottom of the cone should finally be radiated away from the surface of the polar mound and the matter should be settled on the neutron star surface there. From such configurations, we can expect an X-ray spectrum composed of a multi-color blackbody spectrum from the polar cone region and a quasi-single blackbody spectrum from the polar mound region. These spectral properties agree with observations. A combination of a fairly sharp pencil beam and a broad fan beam is expected from the polar cone region, while a broad pencil beam is expected from the polar mound region. With these X-ray beam properties, basic patterns of pulse profiles of X-ray pulsars can be explained too.

中文翻译：

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中子星磁极区的 X 射线发射

研究了X射线脉冲星中子星上X射线发射磁极区的结构，吸积率在10$^{17}$ gs$^{-1} \sim 10^{18}$ gs $^{-1}$。结果表明，在每个极区都出现了一个薄而高、辐射能占主导的、发射 X 射线的极锥。极锥的高度是中子星半径的数倍。由于中子星在极锥中的引力而导致的能量增益超过了由于光子在极锥方位角方向上的扩散而造成的能量损失，大量能量被平流到中子星表面。然后，流动携带的辐射能量应该变得很大，以使得辐射压力克服锥体底部的磁压力。因此，物质应该沿着中子星表面沿切线方向膨胀，拖着磁力线，形成土丘状结构。到锥体底部的平流能量最终应该从极地丘表面辐射出去，物质应该沉降在那里的中子星表面。从这些配置中，我们可以期待由来自极锥区域的多色黑体光谱和来自极丘区域的准单黑体光谱组成的 X 射线光谱。这些光谱特性与观察结果一致。预计极锥区域会出现相当尖锐的笔形光束和宽扇形光束的组合，而极地丘区域则预计会出现较宽的笔形光束。凭借这些 X 射线束特性，