The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field
The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field
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DOI：
10.1051/0004-6361:20052834
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发表时间：
2005-03
影响因子：
6.5
通讯作者：
U. Mitra-Kraev;L. Harra;David R. Williams;Egor Kraev
中科院分区：
文献类型：
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作者：
U. Mitra-Kraev;L. Harra;David R. Williams;Egor Kraev
我们提出的第一个X射线观测恒星耀斑期间的振荡。耀斑发生在活动的M-型矮星AT Mic上，并用XMM-牛顿观测到。用小波分析方法研究了软X射线光变曲线（0.2-12 keV）。耀斑的扩展，平坦的峰值显示了阻尼振荡的明显证据，周期约为750 s，指数阻尼时间约为2000 s，初始相对峰间振幅约为15%。我们认为这种振荡是一种与耀斑环相联系的磁声波驻波，并发现最可能的解释是一种纵向慢模波，其环长为（2.5 ± 0.2）× 1010 cm。测得局部磁场强度为105 ± 50 G。这些值是一致的（振荡无关）火炬冷却时间模型和压力平衡比例尺法。这样的耀斑振荡提供了一个很好的机会，以获得日冕性质，如耀斑环的大小或局部磁场强度，否则空间无法解析的星星。
We present the first X-ray observation of an oscillation during a stellar flare. The flare occurred on the active M-type dwarf AT Mic and was observed with XMM-Newton. The soft X-ray light curve (0.2-12 keV) is investigated with wavelet analysis. The flare's extended, flat peak shows clear evidence for a damped oscillation with a period of around 750 s, an exponential damping time of around 2000 s, and an initial, relative peak-to-peak amplitude of around 15%. We suggest that the oscillation is a standing magneto-acoustic wave tied to the flare loop, and find that the most likely interpretation is a longitudinal, slow-mode wave, with a resulting loop length of (2.5 ± 0.2) × 10 10 cm. The local magnetic field strength is found to be 105 ± 50 G. These values are consistent with (oscillation-independent) flare cooling time models and pressure balance scaling laws. Such a flare oscillation provides an excellent opportunity to obtain coronal properties like the size of a flare loop or the local magnetic field strength for the otherwise spatially-unresolved star.