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arXiv 1206.1377astro-ph.HE
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类γ B1e星HD110432的X射线光变曲线特征

Characterization of the X-ray light curve of the gamma Cas-like B1e star HD110432

Myron A. Smith, Raimundo Lopes de Oliveira, Christian Motch

摘要:

HD 110432(BZ Cru; B1 Ve)是一小群“伽马Cas类似物”中最明亮的成员,它们发射出丰富的硬X射线通量,并被无处不在的“耀斑”所打断。“为了描述这颗恒星的X射线时间历史,我们在2010年进行了一系列的六次RXTE多次访问观测,并在2007年使用XMM-牛顿进行了扩展观测。我们分析了这些新的光变曲线以及2002- 2003年的三个旧的XMM-牛顿观测。RXTE观测分布在五个月内,旨在寻找几个月内的长X射线调制。这些观察确实表明存在一个长周期,P = 226天,振幅为2倍。我们还使用了X射线光变曲线构造XMM-牛顿观测的特征的寿命,强度,和1615耀斑类事件的光变曲线的interflare间隔。在考虑了假阳性事件后,我们推断存在955(2002-2003)和386(2007)事件,我们确定为耀斑。同样,作为对照,我们测量了伽马Cas的XMM-牛顿光变曲线中另外一组541个事件的相同属性,经过类似的校正后,产生了517个耀斑。我们发现HD 110432的耀斑性质与我们的对照组基本相似。在这两种情况下,耀斑强度的分布与对数线性关系最佳拟合。这些分布的斜率和耀斑频率本身都表现出适度的波动。我们发现HD 110432的硬X射线波段的某些耀斑在软波段很弱或没有观测到,反之亦然。光变曲线偶尔也会出现持续数小时的快速曲线下降。我们讨论了存在的长周期和这些耀斑的属性的背景下,两个竞争对手的情况下产生硬X射线,一个磁星盘的相互作用和吸积的斑点到一个二级白矮星。

英文摘要:

HD 110432 (BZ Cru; B1Ve) is the brightest member of a small group of "gamma Cas analogs" that emit copious hard X-ray flux, punctuated by ubiquitous "flares." To characterize the X-ray time history of this star, we made a series of six RXTE multi-visit observations in 2010 and an extended observation with the XMM-Newton in 2007. We analyzed these new light curves along with three older XMM-Newton observations from 2002--2003. Distributed over five months, the RXTE observations were designed to search for long X-ray modulations over a few months. These observations indeed suggest the presence of a long cycle with P = 226 days and an amplitude of a factor of two. We also used X-ray light curves constructed from XMM-Newton observations to characterize the lifetimes, strengths, and interflare intervals of 1615 flare-like events in the light curves. After accounting for false positive events, we infer the presence of 955 (2002-2003) and 386 (2007) events we identified as flares. Similarly, as a control we measured the same attributes for an additional group of 541 events in XMM-Newton light curves of gamma Cas, which after a similar correction yielded 517 flares. We found that the flare properties of HD 110432 are mostly similar to our control group. In both cases the distribution of flare strengths are best fit with log-linear relations. Both the slopes of these distributions and the flaring frequencies themselves exhibit modest fluctuations. We discovered that some flares in the hard X-ray band of HD 110432 were weak or unobserved in the soft band and vice versa. The light curves also occasionally show rapid curve drop offs that are sustained for hours. We discuss the existence of the long cycle and these flare properties in the backdrop of two rival scenarios to produce hard X-rays, a magnetic star-disk interaction and the accretion of blobs onto a secondary white dwarf.

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