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arXiv 2106.05040astro-ph.HEnucl-th
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来自电子俘获的磁星壳加热

Heating in Magnetar Crusts from Electron Captures

Nicolas Chamel, Anthea Francesca Fantina, Lami Suleiman, Julian-Leszek Zdunik, Pawel Haensel

摘要:

磁星持续的热光度及其爆发表明在其外壳中存在着某些内部热源。伴随着磁场衰减的物质压缩可能会引发放热的电子俘获,也可能引发轻元素的致密核融合,这些元素可能是从超新星碎片的回落、从圆盘或从星际介质吸积到表面上的。这种情况与吸积中子星中的地壳深部加热有一些相似之处,尽管物质组成和热力学条件非常不同。考虑到电子运动的朗道-拉比量子化,通过分析确定每个反应可以释放的最大可能热量及其位置。数值结果也提出了使用实验,以及理论核数据。虽然沉积的热量主要由原子质量决定,但发现源的位置对磁场强度非常敏感,从而提供了一种探测磁星内部磁场的新方法。大多数源被发现集中在密度$10^{10}-10^{11}$ g cm $^{-3}$与热功率$W^\infty\sim 10^{35}-10^{36}$ erg/s,发现经验通过比较冷却模拟与观察到的热光度。触发反应所需的磁场变化与已知磁星的年龄一致。这表明电子俘获和密核聚变反应可能是磁星中可行的加热机制。目前的结果提供了一致的微观输入中子星冷却模拟,基于相同的模型,作为基础的M-M状态方程。

英文摘要:

The persistent thermal luminosity of magnetars and their outbursts suggest the existence of some internal heat sources located in their outer crust. The compression of matter accompanying the decay of the magnetic field may trigger exothermic electron captures and, possibly, pycnonuclear fusions of light elements that may have been accreted onto the surface from the fallback of supernova debris, from a disk or from the interstellar medium. This scenario bears some resemblance to deep crustal heating in accreting neutron stars, although the matter composition and the thermodynamic conditions are very different. The maximum possible amount of heat that can be released by each reaction and their locations are determined analytically taking into account the Landau--Rabi quantization of electron motion. Numerical results are also presented using experimental, as well as theoretical nuclear data. Whereas the heat deposited is mainly determined by atomic masses, the locations of the sources are found to be very sensitive to the magnetic field strength, thus providing a new way of probing the internal magnetic field of magnetars. Most sources are found to be concentrated at densities $10^{10}-10^{11}$ g cm$^{-3}$ with heat power $W^\infty\sim 10^{35}-10^{36}$ erg/s, as found empirically by comparing cooling simulations with observed thermal luminosity. The change of magnetic field required to trigger the reactions is shown to be consistent with the age of known magnetars. This suggests that electron captures and pycnonuclear fusion reactions may be a viable heating mechanism in magnetars. The present results provide consistent microscopic inputs for neutron star cooling simulations, based on the same model as that underlying the Brussels-Montreal unified equations of state.

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