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arXiv 0806.1166astro-phnucl-th
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中子星低质量X射线双星MXB 1659-29中地壳的冷却

Cooling of the crust in the neutron star low-mass X-ray binary MXB 1659-29

Edward M. Cackett, Rudy Wijnands, Jon M. Miller, Edward F. Brown, Nathalie Degenaar

摘要:

在准持久性中子星瞬变中,长时间的爆发会导致中子星的地壳被加热到与恒星其他部分失去热平衡。在静止期,地壳又冷却下来。在两个准持续源KS 1731-260和MXB 1659-29中观测到了这种地壳冷却。在这里,我们提出了一个额外的钱德拉观测MXB 1659-29在平静,延长监测基线到6.6年后,爆发结束。这一新的观测结果强烈表明,地壳已经热松弛,温度在1000天内保持一致。用指数加常数模型拟合温度冷却曲线,我们确定了465 +/- 25天的e折叠时间尺度,地壳冷却到恒定的表面温度kT = 54 +/- 2 eV(假设D=10 kpc)。由此,我们推断核心温度在3.5E7-8.3E7 K的范围内(假设D=10 kpc),由于表面成分的不确定性。重要的是,我们测试了两个中子星大气模型以及一个黑体模型,发现地壳的热弛豫时间是独立的选择的模型和假设的距离。

英文摘要:

In quasi-persistent neutron star transients, long outbursts cause the neutron star crust to be heated out of thermal equilibrium with the rest of the star. During quiescence, the crust then cools back down. Such crustal cooling has been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29. Here we present an additional Chandra observation of MXB 1659-29 in quiescence, which extends the baseline of monitoring to 6.6 yr after the end of the outburst. This new observation strongly suggests that the crust has thermally relaxed, with the temperature remaining consistent over 1000 days. Fitting the temperature cooling curve with an exponential plus constant model we determine an e-folding timescale of 465 +/- 25 days, with the crust cooling to a constant surface temperature of kT = 54 +/- 2 eV (assuming D=10 kpc). From this, we infer a core temperature in the range 3.5E7-8.3E7 K (assuming D=10 kpc), with the uncertainty due to the surface composition. Importantly, we tested two neutron star atmosphere models as well as a blackbody model, and found that the thermal relaxation time of the crust is independent of the chosen model and the assumed distance.

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