r过程加热对后退吸积的影响：黑洞-中子星合并与双中子星合并的区别
Imprints of r-process heating on fall-back accretion: distinguishing black hole-neutron star from double neutron star mergers
摘要：
包含两颗中子星（NS-NS）或一颗中子星和一个恒星质量黑洞（NS-BH）的致密双星的合并，很可能是短持续时间伽马射线暴（SGRB）的祖先。一部分> 20%的SGRB之后是暂时延长的（>~分钟长）、可变的X射线发射，这归因于中央引擎的持续活动。后期发动机活动的一个来源是束缚潮汐喷出物的回退吸积;然而，观测到的扩展发射光变曲线并没有跟踪天真预期的、不间断的~t ^{-5/3}幂律衰减，而是显示出通常在爆发后持续数十秒的发射间歇或间隙。在这里，我们重新审视加热的影响，由于快速中子捕获（r-过程）核合成率的回落吸积，使用喷出物的属性从数值相对论模拟NS-BH合并在玩具模型的核加热的动态影响。根据残余黑洞的质量，r过程加热可以印上各种各样的回落曲线形状，从几十秒的暂时平静到回落速率的后期截止。这种行为对于喷出物不同部分所经历的核加热的实际变化是鲁棒的。质量小于~3 Msun的中心黑洞通常会在回退速率上经历绝对截止，而质量大于6 - 8 Msun的黑洞则会出现时间间隙。因此，我们建议，SGRB与扩展排放产生的NS-BH，而不是NS-NS，合并。我们的模型意味着LIGO的NS-BH合并检测率，在稳态下，与NS-NS合并的检测率相当或更高。
英文摘要：
Mergers of compact binaries containing two neutron stars (NS-NS), or a neutron star and a stellar-mass black hole (NS-BH), are likely progenitors of short-duration gamma ray bursts (SGRBs). A fraction >20% of SGRBs are followed by temporally-extended (>~ minute-long), variable X-ray emission, attributed to ongoing activity of the central engine. One source of late-time engine activity is fall-back accretion of bound tidal ejecta; however, observed extended emission light curves do not track the naively-anticipated, uninterrupted ~t^{-5/3} power-law decay, instead showing a lull or gap in emission typically lasting tens of seconds after the burst. Here, we re-examine the impact of heating due to rapid neutron capture (r-process) nucleosynthesis on rate of the fall-back accretion, using ejecta properties obtained from numerical relativity simulations of NS-BH mergers in a toy model for the dynamical influence of nuclear heating. Depending on the mass of the remnant black hole, r-process heating can imprint a variety of fall-back curve shapes, ranging from temporal lulls of up to tens of seconds to complete late-time cut-off in the fall-back rate. This behavior is robust to realistic variations in the nuclear heating experienced by different parts of the ejecta. Central black holes with masses <~ 3 Msun typically experience absolute cut-offs in the fall-back rate, while more massive >6-8 Msun black holes instead show temporal gaps. We thus propose that SGRBs with extended emission arise from NS-BH, rather than NS-NS, mergers. Our model implies a NS-BH merger detection rate by LIGO which, in steady-state, is comparable to or greater than that of NS-NS mergers.
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