A Statistical Study of X-ray Stellar Flares of the M-type Star AT Mic

Stellar flares are violent processes of stellar activity, which have a significant impact on the atmospheric composition and life evolution on exo-planets around the host stars. Stellar flares are observed mainly in the optical and X-ray bands, with sudden increase of the X-ray fluxes as large as several to hundreds of times. M-type stars are the most likely host stars of earth-like planets. Therefore, on one hand, it is of great interest to study the statistical incidence of X-ray flares of M-type stars as far as the search for habitable exo-planets is concerned. On the other hand, the occurrence frequency of X-ray stellar flares, particularly for M stars, is of interest for the estimation of the detection rate of X-ray transients with the CAS's Einstein Probe (EP) mission. We studied the statistical property of X-ray flares from the well-known M-type star AT Mic using the 11-year monitoring data from MAXI. We analyzed the X-ray images, light curves and spectra of the MAXI data on AT Mic and found 10 flares with S/N>3. The statistical distribution of the flare luminosity was obtained. Based on this result, we estimated the occurrence frequency of stellar flares from AT Mic. It is estimated that AT Mic produces about 83 flares with luminosity L_X>10³⁰ erg·s^-1 every year. Einstein Probe satellite can see about 8 flares with more than twice the flare amplitude from AT Mic every year.