Variability in Short Gamma-Ray Bursts: Gravitationally Unstable Tidal Tails
Variability in Short Gamma-Ray Bursts: Gravitationally Unstable Tidal Tails
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DOI：
10.3847/2041-8213/ab9a4e
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
E. Coughlin;E. Coughlin;C. Nixon;J. Barnes;B. Metzger;R. Margutti
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作者：
E. Coughlin;E. Coughlin;C. Nixon;J. Barnes;B. Metzger;R. Margutti
短伽玛射线暴（GRB）被认为是两颗中子星（NS）或一颗中子星和一个恒星质量黑洞（BH）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。利用线性稳定性分析的结果，我们证明了如果组成这些尾的物质被模拟为绝热的，并且有效绝热指数满足γ ≥ 5/3，那么这些尾是引力不稳定的，并且坍缩形成小尺度的结。我们分析估计这些结的属性，包括它们的间距沿着潮汐尾，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γ相等），γ = 2 NS，由BH和线性稳定性分析的预测和不稳定崩溃的节点的分布之间找到协议。这些结返回到BH会导致回落率的变化，这可以表现为GRB光变曲线的变化，以及（取决于不稳定性运行的速度）即时发射。这些结返回引起的后期变化也与在一些伽玛暴中观察到的扩展发射一致。
Short gamma-ray bursts (GRBs) are thought to result from the merger of two neutron stars (NSs) or an NS and a stellar mass black hole (BH). 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-disk 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 ≥ 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, 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 NS, by a BH 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 BH induces variability in the fallback rate, which can manifest as variability in the light curve 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.