PSR J0740+6620 的质量-半径与磁场几何联合推断
Joint Mass-Radius and Magnetic-Geometry Inference of PSR J0740+6620
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- Washington University in St. Louis（华盛顿大学）
- University of Helsinki（赫尔辛基大学）
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中文总结 AI 辅助
本研究联合NICER和XMM-Newton数据推断PSR J0740+6620的质量、半径与磁场几何，发现偏移偶极模型更优，质量约2.06太阳质量、半径约13.3公里，并揭示紧凑X射线足迹指向磁层-发射映射中的缺失物理。
中文摘要 AI 辅助
X射线脉冲轮廓建模可以测量中子星半径，但其物理解释仍受限于对表面热点的高度现象学描述。在此，我们将X射线热点直接与脉冲星磁层结构联系起来，并利用NICER和XMM-Newton的观测数据，对大规模毫秒脉冲星PSR J0740+6620的质量、半径和磁场几何进行联合推断。通过GPU加速实现，我们比较了两种能够产生非对跖发射的低维磁场构型：中心轴对称偶极-四极场和偏移偶极场。在所采用的先验下，偏移偶极模型被明确优先选择，Δln Z=5.65（贝叶斯因子约285），并得出M=2.059^{+0.068}_{-0.069} M_sun和R=13.28^{+1.47}_{-1.07} km，与先前的现象学分析大体一致，同时要求两个极冠近似对称加热。无论是边缘化的偏移偶极后验分布还是与计时兼容的代表性模型，都要求有效的X射线发射足迹远小于以中心偶极校准的标称无力极冠。这种紧凑的足迹无法由我们探索性的光子转换估计重现，反而指向从磁层电流到可观测X射线发射的映射中缺失的物理机制。我们的结果表明，物理动机驱动下的热点可以保持质量-半径推断，同时将热点形态转变为探测脉冲星磁层结构和发射物理的探针。
英文摘要
X-ray pulse-profile modeling can measure neutron-star radii, but its physical interpretation remains limited by the largely phenomenological description of the surface hotspots. Here we connect the X-ray hotspots directly to the pulsar magnetospheric structure and jointly infer the mass, radius, and magnetic geometry of the massive millisecond pulsar PSR J0740+6620 from \emph{NICER} and \emph{XMM-Newton} observations. Using a GPU-accelerated implementation, we compare two low-dimensional magnetic configurations that can produce non-antipodal emission: a centered axisymmetric dipole--quadrupole and a shifted dipole. The shifted-dipole model is decisively favored under the adopted priors, with $Δ\ln Z=5.65$ (Bayes factor $\sim285$), and yields $M=2.059^{+0.068}_{-0.069}\,M_{\odot}$ and $R=13.28^{+1.47}_{-1.07}\,\mathrm{km}$, broadly consistent with previous phenomenological analyses, while requiring nearly symmetric heating of the two polar caps. Both the marginalized shifted-dipole posterior and the timing-compatible representative require an effective X-ray-emitting footprint much smaller than the nominal force-free polar cap calibrated for a centered dipole. This compact footprint is not reproduced by our exploratory photon-conversion estimates and instead points to missing physics in the mapping from magnetospheric currents to observable X-ray emission. Our results show that physically motivated hotspots can preserve the mass--radius inference while turning hotspot morphology into a probe of pulsar magnetospheric structure and emission physics.
