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We have embarked in a systematic study of the X-ray emission in avolume-limited sample of M dwarf stars, in order to explore the full range ofactivity levels present in their coronae and, thus, to understand theconditions in their outer atmospheres and their possible impact on thecircumstellar environment. We identify in a recent catalog of the Gaia objectswithin 10 pc from the Sun all the stars with spectral type between M0 and M4,and search systematically for X-ray measurements of this sample. To this end,we use both archival data (from ROSAT, XMM-Newton, and from the ROentgen Surveywith an Imaging Telescope Array (eROSITA) onboard the RussianSpektrum-Roentgen-Gamma mission) and our own dedicated XMM-Newton observations.To make inferences on the properties of the M dwarf corona we compare the rangeof their observed X-ray emission levels to the flux radiated by the Sun fromdifferent types of magnetic structures: coronal holes, background corona,active regions and cores of active regions. At the current state of ourproject, with more than 90\% of the 10pc M dwarf sample observed in X-rays,only GJ 745 A has no detection. With an upper limit luminosity of log Lx[erg/s] < 25.4 and an X-ray surface flux of log FX,SURF [erg/cm^2/s] < 3.6 GJ745 A defines the lower boundary of the X-ray emission level of M dwarfs.Together with its companion GJ 745 B, GJ 745 A it is the only star in thisvolume-complete sample located in the range of FX,SURF that corresponds to thefaintest solar coronal structures, the coronal holes. The ultra-low X-rayemission level of GJ 745 B (log Lx [erg/s] = 25.6 and log FX,SURF [erg/cm^2/s]= 3.8) is entirely attributed to flaring activity, indicating that, while itscorona is dominated by coronal holes, at least one magnetically activestructure is present and determines the total X-ray brightness and the coronaltemperature of the star.

Complete X-ray census of Mdwarfs in the solar Neighborhood I. GJ 745 AB: Coronal-hole Stars in the 10 pc Sample