Time-variable emission from transiently accreting neutron stars in quiescence due to deep crustal heating
Time-variable emission from transiently accreting neutron stars in quiescence due to deep crustal heating
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DOI：
10.1046/j.1365-8711.2001.04515.x
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发表时间：
2001-01
影响因子：
4.8
通讯作者：
G. Ushomirsky;R. Rutledge
中科院分区：
文献类型：
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作者：
G. Ushomirsky;R. Rutledge
在静止状态下的瞬时吸积中子星1034 erg s21 erg，在几天到几年的时间尺度上，被观测到的强度变化很小。如果静态光度是由热中子星星核心提供动力，核心冷却时间尺度比重现时间长得多，并且不能解释观察到的更快的变化。而爆发时地壳中发生的非平衡反应将能量存款在等密度壳层中，由此向光球的热扩散时间尺度为数天至数年。预测的变化幅度太低，无法解释观察到的变化，除非-正如人们普遍认为的那样-超过中子滴密度的中子是超流体。即使这样，在具有标准核心中微子冷却过程的模型中，由于这种机制而产生的变异性也不到50%--仍然太低，无法解释所报道的变异性。然而，具有快速核心中微子冷却的模型可以在爆发后的几天到几年的时间尺度上产生高达20倍的可变性。因此，只有当快速的核心冷却过程是活跃的，从瞬时吸积中子星观察到的强度变化的因素，可以占这个机制。
Transiently accreting neutron stars in quiescence ðLX & 1034 erg s21Þ have been observed to vary in intensity by factors of few, over time-scales of days to years. If the quiescent luminosity is powered by a hot neutron star core, the core cooling time-scale is much longer than the recurrence time, and cannot explain the observed, more rapid variability. However, the non-equilibrium reactions which occur in the crust during outbursts deposit energy in isodensity shells, from which the thermal diffusion time-scale to the photosphere is days to years. The predicted magnitude of variability is too low to explain the observed variability unless – as is widely believed – the neutrons beyond the neutron-drip density are superfluid. Even then, the variability due to this mechanism in models with standard core neutrino cooling processes is less than 50 per cent – still too low to explain the reported variability. However, models with rapid core neutrino cooling can produce a variability by a factor as great as 20, on time-scales of days to years following an outburst. Thus, the factors of ,few intensity variability observed from transiently accreting neutron stars can be accounted for by this mechanism only if rapid core cooling processes are active.