Kerr黑洞周围 inspiraling热点的偏振特征
Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes
AI总结：
本文提出了一种模拟Kerr时空内等纬度inspiraling热点偏振发射的通用框架，通过参数化四速度剖面，展示了inspiral运动产生的独特观测特征：偏振Stokes Q-U循环模式的预cession和unwinding演变，与稳定轨道上的闭合Q-U环形成鲜明对比。
摘要：
偏振干涉测量是一种用于探测黑洞吸积物理和背景时空的强大工具。目前解释Sgr A*观测到的多波段耀斑的模型通常假设热点沿测地线、开普勒轨道运动。然而在许多情况下，热点可能遵循inspiraling轨迹，最终向黑洞 plunge。本文提出了一种通用框架，利用参数化四速度剖面模拟Kerr时空内等纬度inspiraling热点的偏振发射。该参数化定义了一个连续的流体族，从Cunningham盘模型（固定半径轨道在最内稳定圆轨道外， plunge运动在最内稳定圆轨道内）到纯径向运动，从而扩展了标准假设。在该框架下，我们展示了inspiral运动产生独特的观测特征：Q-U循环模式的预cession和unwinding演变，与固定半径稳定轨道上的闭合Q-U环形成鲜明对比。然后我们探讨了这些特征的形态如何依赖于黑洞自旋、观测者倾角和磁场配置。所提出的模型可用于当前和未来线性偏振干涉测量观测，提供了一种新的途径来探测物质向内螺旋运动的物理和relativistic速度的plunging等离子体。
英文摘要：
Polarimetric interferometry is a powerful tool for probing both black hole accretion physics and the background spacetime. Current models aimed at explaining the observed multiwavelength flares in Sgr A* often assume hotspots moving on geodesic, Keplerian orbits. In many scenarios, though, a hotspot may instead follow an inspiraling trajectory, potentially transitioning into a plunge toward the black hole. In this work, we present a general framework to simulate the polarized emission from generic equatorial inspiraling hotspots in Kerr spacetime using a parametric four-velocity profile. This parametrization defines a continuous family of flows, ranging from Cunningham's disk model (fixed radius orbits outside the innermost stable circular orbit and plunging motion within the innermost stable circular orbit) to purely radial motion, thereby extending the standard assumptions. Within this framework, we show that inspiral motion produces a distinctive observational signature: a precessing, unwinding evolution of the polarimetric Stokes Q-U looping pattern, in sharp contrast with the closed Q-U loops associated with stable orbits at a fixed radius. We then explore how the morphology of these signatures depends on black hole spin, observer inclination, and magnetic-field configuration. The presented model can be applied to current and near-future interferometric observations of linear polarization, offering a new avenue to probe the physics of matter spiraling inward and the relativistic velocities of plunging plasma.
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