短伽马射线暴的变化：引力不稳定的潮汐尾
Variability in Short Gamma-ray Bursts: Gravitationally Unstable Tidal Tails
摘要：
短伽马射线暴被认为是两颗中子星或一颗中子星与恒星质量的黑洞合并的结果。合并的最后阶段通常伴随着喷出物的一个或多个潮汐“尾巴”的产生，这些尾巴在晚些时候落回残留盘系统。使用线性稳定性分析的结果，我们表明，如果这些尾巴的材料被建模为绝热和有效绝热指数满足$γ\ge 5/3$，那么尾巴是引力不稳定和崩溃，形成小规模的结。我们分析估计这些结的属性，包括它们的间距沿潮汐尾和产生的总数，以及它们对合并残余物的质量返回率的影响。我们进行流体动力学模拟的破坏多方（多方和绝热指数PDMATHAMN相等），$γ=2$中子星的黑洞，并找到协议的线性稳定性分析的预测和不稳定性崩溃的结的分布。这些结返回到黑洞会引起回退率的变化，这可以表现为伽玛射线暴的光变曲线的变化，以及--取决于不稳定运行的速度--即时发射。由这些节点的返回引起的后期变率也与在一些GRB中观察到的扩展发射一致。
英文摘要：
Short gamma-ray bursts are thought to result from the mergers of two neutron stars or a neutron star and stellar mass black hole. The final stages of the merger are generally accompanied by the production of one or more tidal "tails" of ejecta, which fall back onto the remnant-disc system at late times. Using the results of a linear stability analysis, we show that if the material comprising these tails is modeled as adiabatic and the effective adiabatic index satisfies $γ\ge 5/3$, then the tails are gravitationally unstable and collapse to form small-scale knots. We analytically estimate the properties of these knots, including their spacing along the tidal tail and the total number produced, and their effect on the mass return rate to the merger remnant. We perform hydrodynamical simulations of the disruption of a polytropic (with the polytropic and adiabatic indices $γ$ equal), $γ=2$ neutron star by a black hole, and find agreement between the predictions of the linear stability analysis and the distribution of knots that collapse out of the instability. The return of these knots to the black hole induces variability in the fallback rate, which can manifest as variability in the lightcurve of the GRB and -- depending on how rapidly the instability operates -- the prompt emission. The late-time variability induced by the return of these knots is also consistent with the extended emission observed in some GRBs.
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