潮汐瓦解事件吸积流中Lense-Thirring进动的啁啾效应
The chirping of Lense-Thirring precession in tidal disruption event accretion flows
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中文总结 AI 辅助
本文研究潮汐瓦解事件吸积盘的Lense-Thirring进动，指出厚盘进动周期因角动量守恒而快速啁啾，导致难以观测多个周期，并影响盘对齐及X射线准周期喷发模型的解释。
中文摘要 AI 辅助
潮汐瓦解事件的X射线光变曲线似乎没有显示出清晰的周期性调制迹象。这从直观上看有些令人惊讶，因为被瓦解的恒星起源于星系中的大尺度区域，在那里它们无法知晓黑洞自转轴的方向。这应当导致形成与黑洞赤道面错位的吸积盘，该吸积盘由于Lense-Thirring力矩而发生进动，从而调制来自内盘区域的X射线发射。我们认为，实际上，固体进动所需的条件，即厚盘（$H/R\sim {\mathcal O}(1)$），自然会导致进动周期快速变化，每个周期的增加量为$\Delta T_{\rm prec}/T_{\rm prec} \sim {\mathcal O}(1-10)$，因为吸积盘为了守恒角动量而向外扩展到更大半径。换句话说，厚TDE吸积盘的进动具有强烈的啁啾效应，从而抹去了观测到多个周期的可能性，除非在参数空间中经过精细调谐的区域。整体盘对齐的时间尺度同样被完全相同的机制强烈啁啾，这意味着TDE吸积盘在超爱丁顿阶段通常不会与黑洞自转轴对齐，并且在任何薄盘阶段开始时通常应表现出全局准稳态的翘曲轮廓。这些结果对于解释与TDE吸积盘相关的时间特征具有重要意义，包括准周期X射线喷发时序现象的模型，以及TDE吸积盘在初始过渡到薄盘阶段时的观测性质。
英文摘要
Tidal disruption event X-ray light curves do not appear to show clear signs of periodic modulation. This is naively somewhat surprising since the stars that are disrupted originate at large scales in the galaxy where they cannot know about the orientation of the black hole spin axis. This should lead to the formation of a misaligned disk that precesses due to Lense-Thirring torques, modulating X-ray emission from the inner disk regions. We argue that in fact the properties which are required for solid-body precession, namely a thick $(H/R\sim {\mathcal O}(1))$ disk, naturally lead to rapid precession period change, with a per-period increase of $ΔT_{\rm prec}/T_{\rm prec} \sim {\mathcal O}(1-10)$, as the disk spreads to larger radii to conserve angular momentum. In other words the precession of thick TDE disks is aggressively chirped, washing out any possibility of observing multiple cycles other than for fine tuned regions of parameter space. The global disk alignment timescale is equally strongly chirped by the exact same mechanism, meaning that TDE disks will not in general align with the black hole spin axis during a super-Eddington phase, and should generically show global quasi-steady warp profiles at the beginning of any thin disk phase. These results have important implications for interpreting timing features associated with TDE disks, including models for quasi-periodic X-ray eruption timing phenomenology, and the observational properties of TDE disks in the initial transition to the thin disk phase.
发表机构
- Institute for Advanced Study（高等研究院）
- Princeton University（普林斯顿大学）
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