发表机构
University of Arizona; Black Hole Initiative at Harvard University（亚利桑那大学; 哈佛大学黑洞倡议）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文利用半解析锥形发射模型，探讨事件视界望远镜及未来任务对黑洞吸积盘偏振螺旋形态$\beta_2$的测量，揭示其约束磁场结构、自旋方向及发射几何的能力。
AI 中文摘要
事件视界望远镜阵列利用所谓的“$\beta_2$”系数测量了黑洞吸积盘的平均偏振螺旋形态。该测量主要由弱透镜效应的直接（$n=0$，计光子半轨道数）图像主导，为研究M87*黑洞周围的磁场结构提供了见解。未来的天基“黑洞探索者”任务预计将扩展这些能力，允许对强透镜效应的$n=1$图像进行$\beta_2$测量。在本文中，我们利用半解析锥形发射模型探讨了$\beta_2$测量对时空和等离子体几何结构的约束。我们表明，磁场相对于发射锥的方向会定性改变$\beta_2$模式对模型参数的依赖关系。对于锥对齐磁场，我们发现来自赤道发射体的领先阶理论预测$\beta_{2,\\,n=0} \approx \beta_{2,\\,n=1}^*$即使在非赤道模型中也是主导趋势。具体而言，我们证明$\arg(\beta_{2,\\,n=0}\\,\beta_{2,\\,n=1}^*) \approx 4\chi$，其中$\chi$是决定锥内磁场方向的角度。我们还发现，$\arg(\beta_{2,\\,n=0}\beta_{2,\\,n=1})$最小化了磁场几何的影响，同时保留了对自旋的依赖，可用于测量自旋方向。我们发现，光子环的$\beta_2$观测补充了直接图像偏振的约束，即使在外部旋转测量未知的情况下，也能极大地约束磁场结构。我们还发现，除非对磁场几何施加强先验，否则仅凭$\beta_2$无法紧密约束黑洞自旋和发射锥张角。
英文摘要
The Event Horizon Telescope array has measured the average polarimetric spiral morphology of black hole accretion disks using the so-called ``$β_2$'' coefficient. This measurement is dominated by the weakly lensed, direct ($n=0$, counting photon half-orbits) image of the disk, providing insight into magnetic field structure around the M87* black hole. The future space-based Black Hole Explorer mission is expected to extend these capabilities, allowing for $β_2$ measurement of the strongly lensed $n=1$ image. In this paper, we explore the constraints $β_2$ measurements would impose on spacetime and plasma geometries using a semi-analytic conical emission model. We show that magnetic field orientation with respect to the emission cone qualitatively changes the dependence of $β_2$ modes on model parameters. For cone-aligned magnetic fields, we find that the leading-order theoretical prediction from equatorial emitters of $β_{2,\, n=0} \approxβ_{2,\, n=1}^*$ is the dominant trend even in off-equatorial models. Specifically, we show $\arg(β_{2,\, n=0}\,β_{2,\, n=1}^*) \approx 4χ$, where $χ$ is the angle determining in-cone magnetic field orientation. We also find that $\arg(β_{2,\, n=0}β_{2,\, n=1})$ minimizes the effect of magnetic field geometry while preserving a dependence on spin that may be used to measure spin direction. We find that observations of the photon ring's $β_2$ complement the constraint from direct image polarization, and can greatly constrain magnetic field structure even with an unknown external rotation measure. We also find that black hole spin and emission cone opening angle would not be tightly constrained by $β_2$ alone, unless strong priors are placed on the magnetic field geometry.
Comments14 pages, 9 figures
