[论文解读] Short gamma-ray bursts from tidal capture and collisions of compact stars in globular clusters

William H. Lee, E. Ramírez-Ruiz+1 more|arXiv (Cornell University)|Sep 15, 2009

Gamma-ray bursts and supernovae被引用 2

一句话总结

本文提出，短伽马射线暴（SGRBs）可能起源于球状星团核心中致密星体的潮汐捕获与碰撞，而非由引力波辐射驱动的双星并合产生。通过详细的恒星动力学与流体动力学建模，作者表明这些事件可释放足够能量并产生足够事件率，与观测到的SGRB事件率及红移分布相匹配。

ABSTRACT

A new mechanism is proposed by which short gamma-ray burst (SGRB) production can be achieved. In this new paradigm, it is supposed that the compact objects contained within a globular cluster (GC) interact through close encounters, rather than being driven together by pure gravitational wave emission in existing binaries. The corresponding event rates within galaxies have previously been shown to be much too low to be of interest. Here we perform a careful assessment of the relevant processes and stellar dynamics within GCs as these undergo core collapse over cosmic time. We show that such events are frequent enough in their cores to be consistent both with current observational rate demands for SGRB production and with the widening range of observed redshifts of the associated hosts. Precise modeling of the hydrodynamics allows for a detailed description of the encounter, and our calculations show that there is in principle no problem in accounting for the global energy budget of a typical SGRB. The particulars of each collision, however, are variable in several aspects, and can lead to interesting diversity. First and most importantly, the characteristics of the encounter are highly dependent on the impact parameter. This is in contrast to the merger scenario, where the masses of the compact objects dictate a typical length and luminosity scale for SGRB activity. Second,

研究动机与目标

• 调查球状星团核心中致密星体的潮汐捕获与碰撞是否能以可观测的速率产生短伽马射线暴（SGRBs）。
• 评估典型SGRB的能量预算是否可由此类动力学相遇解释。
• 评估撞击参数与相遇几何对塑造SGRB特性的影响，与标准并合场景进行对比。
• 确定此类过程的事件率是否与当前对SGRB宿主星系红移与总体事件率的观测约束一致。

提出的方法

• 模拟经历核心坍缩的球状星团内部的恒星动力学，以估算致密天体的相遇率。
• 模拟致密星体近距离相遇时的流体动力学相互作用，以评估能量释放与喷流特性。
• 计算SGRB的光度与时标对撞击参数与恒星质量的依赖关系。
• 使用数值模拟评估总能量输出，并与典型SGRB的观测能量预算进行比较。
• 通过积分星团群体与核心坍缩演化过程，评估星系中的事件率。
• 将预测的SGRB宿主红移分布与观测结果对比，以检验一致性。

实验结果

研究问题

• RQ1 球状星团核心中致密星体的潮汐捕获与碰撞能否产生能量特性与观测一致的SGRB？
• RQ2 致密星体相遇的撞击参数如何影响所产生的SGRB光度与持续时间？
• RQ3 此类碰撞的预测事件率是否与SGRB宿主的观测事件率及红移分布一致？
• RQ4 此类相遇的动力学与流体动力学特性与双星并合场景有何不同？
• RQ5 典型SGRB的能量预算是否可完全由此类碰撞中释放的动能解释？

主要发现

• 球状星团核心中致密星体的潮汐捕获与碰撞可产生能量特性与观测一致的SGRB。
• 每次事件的能量输出高度依赖于撞击参数，导致SGRB特性具有内在多样性。
• 此类动力学相遇的事件率足够高，可与当前对SGRB事件率与红移分布的观测约束相匹配。
• 流体动力学模拟证实，典型SGRB的总能量预算可由此类碰撞解释。
• 该机制为SGRB产生提供了一种可行的替代方案，尤其在致密天体密度较高的环境中。
• 由于撞击参数导致的相遇结果差异，产生了多种SGRB光度与时标，与观测到的多样性一致。