2020ApJ...890...46T

Superflares, which are strong explosions on stars, have been well studied with the progress of spacetime-domain astronomy. In this work, we present the study of superflares on solar-type stars using Transiting Exoplanet Survey Satellite (TESS) data. Thirteen sectors of observations during the first year of the TESS mission covered the southern hemisphere of the sky, containing 25,734 solar-type stars. We verified 1216 superflares on 400 solar-type stars through automatic search and visual inspection with 2 minute cadence data. Our result suggests a higher superflare frequency distribution than the result from Kepler. This may be because the majority of TESS solar-type stars in our data set are rapidly rotating stars. The power-law index γ of the superflare frequency distribution (dN/dE∝E^-γ^) is constrained to be γ = 2.16 ± 0.10, which is a little larger than that of solar flares but consistent with the results from Kepler. Because only seven superflares of Sun-like stars are detected, we cannot give a robust superflare occurrence frequency. Four stars were accompanied by unconfirmed hot planet candidates. Therefore, superflares may possibly be caused by stellar magnetic activities instead of planet-star interactions. We also find an extraordinary star, TIC43472154, which exhibits about 200 superflares per year. In addition, the correlation between the energy and duration of superflares (T_duration∝E^β^) is analyzed. We derive the power-law index to be β = 0.42 ± 0.01, which is a little larger than β = 1/3 from the prediction according to magnetic reconnection theory.