发表机构
School of Physics, Peking University（北京大学物理学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究提出改进的扁球-施瓦西解析模型，用于计算旋转中子星热X射线脉冲轮廓，相比球形模型显著提高与射线追踪的一致性，同时保持解析计算效率。
AI 中文摘要
热X射线脉冲轮廓通过引力光弯曲和旋转对表面发射的影响来约束中子星的质量和半径。增强型X射线定时与偏振（eXTP）任务预期达到的精度促使我们开发更精确的解析光弯曲公式，同时保持重复模型评估所需的效率。我们在扁球-施瓦西（OS）近似下推导了一个改进的解析通量表达式，该表达式结合了弯曲、传播延迟和透镜近似以及球状表面。我们将该模型的轮廓与数值施瓦西和二阶Hartle-Thorne射线追踪在同一球状表面上进行比较。比较采用选定的双点配置，频率为300 Hz，各向同性黑体发射，并考虑三种表面偏心率选择：自由指定值、均匀旋转牛顿流体的Maclaurin关系以及旋转中子星表面的拟合值。在这些情况下，改进的OS轮廓相对于Hartle-Thorne参考的RMS通量差异为1.76%-1.98%，而球形施瓦西加多普勒（S+D）模型的差异为6.50%-21.39%。所有差异均归一化到相位平均参考通量。施瓦西与Hartle-Thorne射线追踪之间的相应差异保持在1.1%以下。这些比较将解析光子传输中的误差与表面变形和旋转外部时空的影响分开。对于所检查的配置，考虑扁率显著提高了与射线追踪的一致性。该模型保留了解析计算的速度，同时使轮廓变化的物理起源变得明确。
英文摘要
Thermal X-ray pulse profiles constrain neutron-star masses and radii through the effects of gravitational light bending and rotation on surface emission. The precision anticipated from the enhanced X-ray Timing and Polarimetry (eXTP) mission motivates more accurate analytic light-bending formulae that retain the efficiency needed for repeated model evaluations. We derive a refined analytic flux expression within the oblate--Schwarzschild (OS) approximation that combines bending, propagation-delay, and lensing approximations with a spheroidal surface. We compare its profiles with numerical Schwarzschild and second-order Hartle--Thorne ray tracing on the same spheroidal surfaces. The comparisons use a selected two-spot configuration at 300 Hz with isotropic blackbody emission and three choices for surface eccentricity: a freely specified value, the Maclaurin relation for a uniformly rotating Newtonian fluid, and a fit to rotating-neutron-star surfaces. Across these cases, the refined OS profiles have RMS flux differences of $1.76-1.98\%$ relative to the Hartle--Thorne reference, compared with $6.50-21.39\%$ for the spherical Schwarzschild-plus-Doppler (S+D) model. All differences are normalized to the phase-averaged reference flux. The corresponding differences between Schwarzschild and Hartle--Thorne ray tracing remain below $1.1\%$. These comparisons separate errors in analytic photon transfer from the effects of surface deformation and the rotating exterior spacetime. For the configurations examined, accounting for oblateness substantially improves agreement with ray tracing. The model retains the speed of an analytic calculation while making the physical origin of profile changes explicit.
