Flaring activity of Proxima Centauri from TESS observations: quasi-periodic oscillations during flare decay and inferences on the habitability of Proxima b.

We analyze the light curve of the M5.5 dwarf Proxima Centauri obtained by the TESS in Sectors 11 and 12. In the $\approx 50$ day-long light curve we identified and analyzed 72 flare events. The flare rate was 1.49 events per day, in total, 7.2% of the data was classified as flaring. The estimated flare energies were in the order of $10^{30}-10^{32}$ ergs in the TESS passband. Most of the eruptions appeared in groups. Two events showed quasi-periodic oscillations during their decay phase with a time scale of a few hours, that could be caused by quasiperiodic motions of the emittimg plasma or oscillatory reconnection. From the cumulative flare frequency distribution we estimate that superflares with energy output of $10^{33}$ ergs are expected to occur 3 times per year, while a magnitude larger events (with $10^{34}$ ergs) can occur every second year. This reduces the chances of habitability of Proxima Cen b, although earlier numerical models did not rule out the existence of liquid water on the planetary surface. We did not find any obvious signs of planetary transit in the light curve.