2025ApJ...993..212N

We present the X-ray quiescent and flaring properties from a unique, 7 days multiwavelength observing campaign on the M1 flare star AU Mic. Combining the XMM-Newton X-ray spectra with the chromospheric line and broadband near-UV (NUV) and optical continuum observations provides a data set 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 >10³³ erg. The T-EM evolution tracks and multiwavelength 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 Hα and Hβ 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 Hα and Hβ broadenings with roughly ±400 and ±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 Hα and Hβ 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.