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The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field

U. Mitra-Kraev·L. K. Harra·D. R. Williams·E. Kraev
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Abstract

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) e10 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.

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U. Mitra-Kraev, L. K. Harra, D. R. Williams, E. Kraev. 2005-03-17. The first observed stellar X-ray flare oscillation: Constraints on the flare loop length and the magnetic field. https://doi.org/10.1051/0004-6361%3A20052834

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