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首页> 外文期刊>Astronomy and astrophysics >A survey of stellar X-ray flares from the XMM-Newton serendipitous source catalogue: HIPPARCOS-Tycho cool stars
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A survey of stellar X-ray flares from the XMM-Newton serendipitous source catalogue: HIPPARCOS-Tycho cool stars

机译：来自XMM-牛顿偶然来源目录的恒星X射线耀斑的调查：HIPPARCOS-Tycho酷星

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Context. The X-ray emission from flares on cool (i.e. spectral-type F–M) stars is indicative of very energetic, transient phenomena, associated with energy release via magnetic reconnection. Aims. We present a uniform, large-scale survey of X-ray flare emission. The XMM-Newton Serendipitous Source Catalogue and its associated data products provide an excellent basis for a comprehensive and sensitive survey of stellar flares – both from targeted active stars and from those observed serendipitously in the half-degree diameter field-of-view of each observation. Methods. The 2XMM Catalogue and the associated time-series (“light-curve”) data products have been used as the basis for a survey of X-ray flares from cool stars in the Hipparcos-Tycho-2 catalogue. In addition, we have generated and analysed spectrally-resolved (i.e. hardness-ratio), X-ray light-curves. Where available, we have compared XMM OM UV/optical data with the X-ray light-curves. Results. Our sample contains ~130 flares with well-observed profiles; they originate from ~70 stars. The flares range in duration from ~103 to ~104 s, have peak X-ray fluxes from ~10-13 to ~10-11erg cm-2 s-1, peak X-ray luminosities from ~1029 to ~1032erg s-1, and X-ray energy output from ~1032 to ~1035 erg. Most of the ~30 serendipitously-observed stars have little previously reported information. The hardness-ratio plots clearly illustrate the spectral (and hence inferred temperature) variations characteristic of many flares, and provide an easily accessible overview of the data. We present flare frequency distributions from both target and serendipitous observations. The latter provide an unbiased (with respect to stellar activity) study of flare energetics; in addition, they allow us to predict numbers of stellar flares that may be detected in future X-ray wide-field surveys. The serendipitous sample demonstrates the need for care when calculating flaring rates, especially when normalising the number of flares to a total exposure time, where it is important to consider both the stars seen to flare and those from which variability was not detected (i.e. measured as non-variable), since in our survey, the latter outnumber the former by more than a factor ten. The serendipitous variable and “non-variable” stars appear very similar in terms of the distributions of general properties such as quiescent X-ray luminosity; from the available data, it is unclear whether the distinction by flaring is due to an additional, intrinsic property such as intra-system interactions in a close binary system, or is simply the result of limited observations and detection thresholds on a random flaring process, with no real difference between the two samples, or may be a combination of these effects. However, the number of detected flares compared with the number of stars not seen to vary is broadly consistent with estimates based on Poisson statistics.
机译：上下文。来自冷恒星（即光谱型FM）的耀斑的X射线发射表明非常活跃的瞬态现象，与通过磁重新连接释放出的能量有关。目的我们提出了一个统一的，大规模的X射线耀斑发射调查。 XMM-牛顿偶发源目录及其相关数据产品为全面，敏感地调查恒星耀斑奠定了良好的基础-既来自目标活跃恒星，又来自每次观测的半度直径视野中偶然发现的恒星。方法。 2XMM目录和相关的时间序列（“光曲线”）数据产品已用作调查Hipparcos-Tycho-2目录中来自冷恒星的X射线耀斑的基础。此外，我们还生成并分析了光谱分辨（即硬度比）的X射线光曲线。如果可以的话，我们将XMM OM UV /光学数据与X射线光曲线进行了比较。结果。我们的样本包含〜130个耀斑，轮廓清晰可见;它们起源于70颗星。耀斑的持续时间从〜103到〜104 s，X射线通量峰值从〜10-13到〜10-11erg cm-2 s-1，峰值X射线光度从〜1029到〜1032erg s-1 ，X射线能量输出从〜1032到〜1035 erg。大约30个偶然观测到的恒星中，大多数以前没有报道过的信息。硬度比图清楚地说明了许多耀斑的光谱（并因此推断出温度）的变化特征，并提供了易于访问的数据概览。我们从目标和偶发观测中介绍了耀斑频率分布。后者提供了关于耀斑能量学的无偏见（就恒星活动而言）。此外，它们还使我们能够预测在将来的X射线宽视场勘测中可能发现的恒星耀斑数量。意外样本证明了在计算耀斑率时需要小心，尤其是在将耀斑数量标准化为总暴露时间时，必须同时考虑到看到耀斑的恒星和未发现变异的恒星（即不变），因为在我们的调查中，后者比前者多十倍。就一般特性（例如静态X射线光度）的分布而言，偶然的可变星和“不变”星看起来非常相似。根据现有数据，目前尚不清楚扩口的区别是由于其他固有特性，例如紧密二元系统中的系统内相互作用，还是仅仅是由于随机扩口过程中观察和检测阈值有限而导致的，两个样本之间没有真正的差异，或者可能是这些影响的组合。然而，与未见变化的恒星数量相比，探测到的耀斑数量与基于泊松统计的估计大致一致。

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