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arXiv · 2509.06908

A Seven-Day Multi-Wavelength Flare Campaign on AU Mic III: Quiescent and Flaring Properties of the X-ray Spectra and Chromospheric lines

Yuta Notsu·Isaiah I. Tristan·Rachel A. Osten·Alexander Brown·Adam F. Kowalski·Carol A. Grady
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Abstract

We present the X-ray quiescent and flaring properties from a unique, 7-day multiwavelength observing campaign on the M1 flare star AU Mic. Combining the XMM-Newton X-ray spectra with the chromospheric line and broadband NUV and optical continuum observations provides a dataset that is one of the most comprehensive to date. We analyze the sample of 38 X-ray flares and study in detail the X-ray flare temperature ($T$) and emission measure (EM) evolutions of three largest flares with the X-ray flare energies of $>10^{33}$ erg. The $T-\mathrm{EM}$ evolution tracks and multi-wavelength emission evolutions of the largest-amplitude Neupert-type flare reveal that the so-called ``Flare H-R diagram" is consistent with thermal coronal flare emission evolution. The two other more gradual and longer duration X-ray flares are interpreted as having larger size scales. None of the 17 H$\alpha$ and H$\beta$ flares show clear blue/red wing asymmetries, including the ones associated with the potential X-ray dimming event previously reported. The above largest-amplitude Neupert flare shows clear symmetric H$\alpha$ and H$\beta$ broadenings with roughly $\pm$400 and $\pm$600 km s$^{-1}$, respectively, which are synchronized with the optical/NUV continuum emission evolution. Radiative hydrodynamic modeling results suggest that electron beam heating parameters that have been used to reproduce M-dwarf flare NUV/optical continuum emissions can reproduce these large broadenings of H$\alpha$ and H$\beta$ lines. These results suggest that these most energetic M-dwarf flares are associated with stronger magnetic field flux densities and larger size scales than solar flares but can be interpreted in terms of the standard flare model.

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Yuta Notsu, Isaiah I. Tristan, Rachel A. Osten, Alexander Brown, Adam F. Kowalski, Carol A. Grady. 2025-09-08. A Seven-Day Multi-Wavelength Flare Campaign on AU Mic III: Quiescent and Flaring Properties of the X-ray Spectra and Chromospheric lines. https://doi.org/10.3847/1538-4357%2Fae0578

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