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arXiv 2104.01181astro-ph.HE
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由双中子星合并产生的超大质量中子星的生存时间

Survival times of supramassive neutron stars resulting from binary neutron star mergers

Paz Beniamini, Wenbin Lu

摘要:

双星中子星(BNS)合并可能导致各种结果,从无限稳定的中子星,到超大质量(SMNS)或超大质量(HMNS)中子星,只是暂时对抗重力,到合并后迅速形成的黑洞。对BNS总质量和中子星状态方程的最新约束表明,在BNS合并的$\sim 0.45-0.9$中可能形成长寿命的SMNS。一个最大旋转的SMNS需要在它坍缩之前失去它的旋转能量的$\sim 3-6\times 10^{52}$ erg,在自旋下降时间尺度的一小部分上。一个SMNS编队印记在电磁对应的BNS合并。然而,与观察结果的比较揭示了紧张局势。首先,坍缩时间的分布太宽,释放的能量太窄(能量本身太大),无法解释观察到的内部X射线平台的分布,作为SMNS能量注入的证据。其次,巨大的能量注入冲击波应该会导致非常明亮的无线电瞬变,以前的研究发现这与短伽马射线暴的深层无线电观测不一致。此外,我们表明,即将到来的全天空无线电调查将限制提取的能量分布,独立的伽玛射线暴喷流形成。我们的结果可以自我一致地理解,只要大多数BNS合并残留物在形成后不久崩溃(即使它们的质量足够低,允许SMNS形成)。如果残余物在进入固体旋转时保持其初始能量的一半或更少,这自然会发生。

英文摘要:

A binary neutron star (BNS) merger can lead to various outcomes, from indefinitely stable neutron stars, through supramassive (SMNS) or hypermassive (HMNS) neutron stars supported only temporarily against gravity, to black holes formed promptly after the merger. Up-to-date constraints on the BNS total mass and the neutron star equation of state suggest that a long-lived SMNS may form in $\sim 0.45-0.9$ of BNS mergers. A maximally rotating SMNS needs to lose $\sim 3-6\times 10^{52}$ erg of it's rotational energy before it collapses, on a fraction of the spin-down timescale. A SMNS formation imprints on the electromagnetic counterparts to the BNS merger. However, a comparison with observations reveals tensions. First, the distribution of collapse times is too wide and that of released energies too narrow (and the energy itself too large) to explain the observed distributions of internal X-ray plateaus, invoked as evidence for SMNS-powered energy injection. Secondly, the immense energy injection into the blastwave should lead to extremely bright radio transients which previous studies found to be inconsistent with deep radio observations of short gamma-ray bursts. Furthermore, we show that upcoming all-sky radio surveys will constrain the extracted energy distribution, independently of a GRB jet formation. Our results can be self-consistently understood, provided that most BNS merger remnants collapse shortly after formation (even if their masses are low enough to allow for SMNS formation). This naturally occurs if the remnant retains half or less of its initial energy by the time it enters solid body rotation.

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