中央致密天体有碳大气层吗？
Do Central Compact Objects have Carbon Atmospheres?
摘要：
超新星遗迹（SNRs）中的十几个中心致密天体（CCO）中只有三个显示出由于不均匀的表面温度（热点）而引起的热X射线脉动。几个无脉冲的CCO没有X射线脉动，这促使人们认为它们有均匀温度的碳气氛（UTCA），这使它们的光谱与适当的中子星（NS）表面积充分吻合。这与同样适合的双温度黑体或氢气氛形成对比。在这里，我们调查UTCA的适用性CCO。我们显示以下内容：（i）三个脉冲CCO的相位平均光谱也可以用适当NS面积的UTCA拟合，尽管脉冲CCO明显具有不均匀的表面温度。因此，良好的光谱拟合不是对非脉冲CCO的UTCA模型的有力支持。(ii)先前使用UTCA分析的一个非脉冲CCO的改进光谱不允许可接受的拟合。(iii)对于两个非脉冲CCO，UTCA不允许与SNR距离兼容的距离。这些结果意味着，在一般情况下，CCO必须有热的，本地化的NS表面上的区域。我们推导出新的X射线脉冲调制上限的非脉冲CCO，并限制其热点的大小和位置。我们开发了一种替代模型，占脉冲和非脉冲CCO：热点和旋转轴之间的角度范围与指数分布与比例因子$λ\sim 20^{\circ}$一致。我们将讨论产生这种小角度和小热点的物理机制。
英文摘要：
Only three of the dozen central compact objects (CCOs) in supernova remnants (SNRs) show thermal X-ray pulsations due to non-uniform surface temperature (hot-spots). The absence of X-ray pulsations from several unpulsed CCOs has motivated suggestions that they have uniform-temperature carbon atmospheres (UTCAs), which adequately fit their spectra with appropriate neutron star (NS) surface areas. This is in contrast to the two-temperature blackbody or hydrogen atmospheres that also fit well. Here we investigate the applicability of UTCAs to CCOs. We show the following: (i) The phase-averaged spectra of the three pulsed CCOs can also be fitted with a UTCA of the appropriate NS area, despite pulsed CCOs manifestly having non-uniform surface temperature. A good spectral fit is therefore not strong support for the UTCA model of unpulsed CCOs. (ii) An improved spectrum of one unpulsed CCO, previously analyzed with a UTCA, does not allow an acceptable fit. (iii) For two unpulsed CCOs, the UTCA does not allow a distance compatible with the SNR distance. These results imply that, in general, CCOs must have hot, localized regions on the NS surface. We derive new X-ray pulse modulation upper limits on the unpulsed CCOs, and constrain their hot spot sizes and locations. We develop an alternative model that accounts for both the pulsed and unpulsed CCOs: a range of angles between hot spot and rotation axes consistent with an exponential distribution with scale factor $λ\sim 20^{\circ}$. We discuss physical mechanisms that could produce such small angles and small hot-spots.
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