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arXiv 1809.01419astro-ph.HE
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γ Cas和HD110432的Suzaku和NuSTAR X射线光谱

Suzaku and NuSTAR X-Ray Spectroscopy of gamma Cas and HD110432

Masahiro Tsujimoto, Kumiko Morihana, Takayuki Hayashi, Takao Kitaguchi

摘要:

伽玛射线和它的十几个类似物组成了一个小的,但独特的X射线源的类别。它们是早期的Be型恒星,具有异常坚硬的热X射线发射。X射线的产生机制一直处于激烈的争论之中。两个相互竞争的观点是(i)Be星及其盘的磁活动和(ii)未被确认的白矮星(WD)的质量吸积。我们采用后者作为一个工作假设,并应用物理模型来描述的X射线光谱的经典WD双星包含一个晚型的同伴。非磁性和磁性吸积WD的模型被应用到伽马Cas和其最明亮的模拟HD110432使用朱雀和NuSTAR数据。用两种模型对光谱进行了拟合,其中包括Fe I荧光和康普顿反射的几何一致性。所导出的物理参数,如WD质量和质量吸积率,是在一个合理的范围内相比,他们的经典WD二元对应。在X射线光谱(部分覆盖,铁L线,和铁I荧光)的其他证据不足以将这两个来源归类为一个子类的吸积WD双星。我们讨论了进一步的观察,特别是长期的时间行为,这是重要的阐明这些来源的性质,如果他们确实主机吸积WD。

英文摘要:

Gamma Cas and its dozen analogs comprise a small but distinct class of X-ray sources. They are early Be-type stars with an exceptionally hard thermal X-ray emission. The X-ray production mechanism has been under intense debate. Two competing ideas are (i) the magnetic activities in the Be star and its disk and (ii) the mass accretion onto the unidentified white dwarf (WD). We adopt the latter as a working hypothesis and apply physical models developed to describe the X-ray spectra of classical WD binaries containing a late-type companion. Models of non-magnetic and magnetic accreting WDs were applied to gamma Cas and its brightest analog HD110432 using the Suzaku and NuSTAR data. The spectra were fitted by the two models, including the Fe I fluorescence and the Compton reflection in a consistent geometry. The derived physical parameters, such as the WD mass and mass accretion rate, are in a reasonable range in comparison to their classical WD binary counterparts. Additional pieces of evidence in the X-ray spectra (partial covering, Fe L lines, and Fe I fluorescence) were not conclusive enough to classify these two sources into a sub-class of accreting WD binaries. We discuss further observations, especially long-term temporal behaviors, which are important to elucidate the nature of these sources more if indeed they host accreting WDs.

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