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arXiv 1403.2385astro-ph.HE
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探测EXO 0748-676中子星的地壳

Probing the Crust of the Neutron Star in EXO 0748-676

N. Degenaar, Z. Medin, A. Cumming, R. Wijnands, M. T. Wolff, E. M. Cackett, J. M. Miller, P. G. Jonker, J. Homan, E. F. Brown

摘要:

对静止X射线双星的X射线观测有可能提供对中子星结构和组成的深入了解。EXO 0748-676在2008年底停止爆发之前已经活跃了超过24年。随后的X射线监测显示,静态热辐射逐渐衰减,这可以归因于吸积加热的中子星地壳的冷却。在这项工作中,我们报告了新的钱德拉和斯威夫特的意见,延长静止监测到5年后爆发。我们发现,中子星的温度在2009年至2011年期间保持在~117 eV,但在2013年下降到~110 eV。这表明地壳还没有完全冷却,这是由1980年吸积阶段之前约4年测量的~95 eV的较低温度支持的。将这些数据与热演化模拟进行比较后发现,2009年至2011年期间明显缺乏冷却可能是中子星外层轻核和重核相分离驱动的对流的特征。

英文摘要:

X-ray observations of quiescent X-ray binaries have the potential to provide insight into the structure and the composition of neutron stars. EXO 0748-676 had been actively accreting for over 24 yr before its outburst ceased in late 2008. Subsequent X-ray monitoring revealed a gradual decay of the quiescent thermal emission that can be attributed to cooling of the accretion-heated neutron star crust. In this work, we report on new Chandra and Swift observations that extend the quiescent monitoring to ~5 yr post-outburst. We find that the neutron star temperature remained at ~117 eV between 2009 and 2011, but had decreased to ~110 eV in 2013. This suggests that the crust has not fully cooled yet, which is supported by the lower temperature of ~95 eV that was measured ~4 yr prior to the accretion phase in 1980. Comparing the data to thermal evolution simulations reveals that the apparent lack of cooling between 2009 and 2011 could possibly be a signature of convection driven by phase separation of light and heavy nuclei in the outer layers of the neutron star.

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