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arXiv 0711.4207astro-ph
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经典低质量X射线双星瞬变的第一次超暴

First superburst from a classical low-mass X-ray binary transient

L. Keek, J. J. M. in 't Zand, E. Kuulkers, A. Cumming, E. F. Brown, M. Suzuki

摘要:

利用Rossi X射线定时探测器上的全天监视器(ASM)对一个瞬态吸积中子星系统的首次超暴进行了分析。超级爆发发生在4U 1608-522的吸积爆发开始后55天。在这段时间内,吸积率至少是爱丁顿极限的7%。超暴的峰值通量是爱丁顿极限的22%到45%,其辐射能量输出在4 e41和9 e41尔格之间,距离为3.2 kpc。冷却模型与超爆发光曲线的拟合表明,点火柱深度在1.5e12和4.1e12 g/cm 2之间。外推由ASM观察到的吸积历史,我们得出这个列是在26至72年的时间内吸积。超暴特征与其他超暴低质量X射线双星的特征一致。然而,宿主双星的瞬态性质对超暴理论提出了重大挑战,需要为模型添加额外的成分。超级爆发的燃料碳被认为主要是在吸积爆发期间产生的,并在频繁的I型X射线爆发中被破坏。中子星包层中元素的混合和沉积可能会显著影响碳的生成和破坏之间的平衡。此外,对中子星地壳温度的预测未能达到在推断的柱深度处点燃碳所需的值。

英文摘要:

We report the analysis of the first superburst from a transiently accreting neutron star system with the All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer. The superburst occurred 55 days after the onset of an accretion outburst in 4U 1608-522. During that time interval, the accretion rate was at least 7% of the Eddington limit. The peak flux of the superburst is 22 to 45% of the Eddington limit, and its radiation energy output is between 4e41 and 9e41 erg for a distance of 3.2 kpc. Fits of cooling models to the superburst light curve indicate an ignition column depth between 1.5e12 and 4.1e12 g/cm2. Extrapolating the accretion history observed by the ASM, we derive that this column was accreted over a period of 26 to 72 years. The superburst characteristics are consistent with those seen in other superbursting low-mass X-ray binaries. However, the transient nature of the hosting binary presents significant challenges for superburst theory, requiring additional ingredients for the models. The carbon that fuels the superburst is thought to be produced mostly during the accretion outbursts and destroyed in the frequent type-I X-ray bursts. Mixing and sedimentation of the elements in the neutron star envelope may significantly influence the balance between the creation and destruction of carbon. Furthermore, predictions for the temperature of the neutron star crust fail to reach the values required for the ignition of carbon at the inferred column depth.

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