利用Hills机制产生重复的局部潮汐扰动事件和ASASSN-14 ko
Using the Hills Mechanism to Generate Repeating Partial Tidal Disruption Events and ASASSN-14ko
摘要：
周期性的核瞬变现象越来越频繁地被探测到，其中一个这样的系统-- ASASSN-14 ko--在$114 \pm 1$天的时间尺度上表现出高度规则的爆发。人们假设，这个来源的爆发是由恒星的重复部分破裂产生的，但恒星是如何被放置在围绕超大质量黑洞的如此紧密的轨道上仍然不清楚。在这里，我们使用的分析参数和三体积分证明，希尔斯机制，其中一个二元系统被摧毁的黑洞的潮汐，可以导致捕获一颗恒星的$\sim 114$日轨道和近心距离，相当于潮汐半径的恒星之一的二进制。因此，希尔斯捕获可以产生在紧密束缚轨道上的恒星，这些恒星经历反复的部分破坏，从而产生一种可行的机制，不仅可以产生从ASASSN-14 ko检测到的爆发，而且可以产生一般的周期性核瞬变。我们还表明，由于引力波发射捕获的恒星周期的变化率可能太小，无法产生ASASSN-14 ko的观测值，这表明在这个系统中，必须有额外的影响，有助于轨道的衰减。然而，一般来说，引力波发射对于限制这些系统的寿命是很重要的，并且可以在未来的事件中产生可观测的周期衰减率。
英文摘要：
Periodic nuclear transients have been detected with increasing frequency, with one such system -- ASASSN-14ko -- exhibiting highly regular outbursts on a timescale of $114 \pm 1$ days. It has been postulated that the outbursts from this source are generated by the repeated partial disruption of a star, but how the star was placed onto such a tightly bound orbit about the supermassive black hole remains unclear. Here we use analytic arguments and three-body integrations to demonstrate that the Hills mechanism, where a binary system is destroyed by the tides of the black hole, can lead to the capture of a star on a $\sim 114$ day orbit and with a pericenter distance that is comparable to the tidal radius of one of the stars within the binary. Thus, Hills capture can produce stars on tightly bound orbits that undergo repeated partial disruption, leading to a viable mechanism for generating not only the outbursts detected from ASASSN-14ko, but for periodic nuclear transients in general. We also show that the rate of change of the period of the captured star due to gravitational-wave emission is likely too small to produce the observed value for ASASSN-14ko, indicating that in this system there must be additional effects that contribute to the decay of the orbit. In general, however, gravitational-wave emission can be important for limiting the lifetimes of these systems, and could produce observable period decay rates in future events.
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