Superflares on solar-type stars from the first year observation of TESS

Abstract

Superflares, as strong explosions on stars, have been well studied with the progress of space time-domain astronomy. In this work, we present the study of superflares on solar-type stars using Transiting Exoplanet Survey Satellite ({\em{TESS}}) data. 13 sectors of observations during the first year of the {\em TESS} mission have covered the southern hemisphere of the sky, containing 25,734 solar-type stars. We verified 1,216 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 {\em Kepler}. The reason may be that the majority of {\em TESS} solar-type stars in our dataset are rapidly rotating stars. The power-law index ${\hat{I}}^3$ of the superflare frequency distribution ($dN/dE\propto E^{-{\hat{I}}^3}$) is constrained to be ${\hat{I}}^3=2.16\pm 0.10$, which is a little larger than that of solar flares but consistent with the results from {\em Kepler}. Because only 7 superflares of Sun-like stars are detected, we may not give a robust superflare occurrence frequency. And four stars are accompanied by unconfirmed hot planet candidates. Therefore, superflares are possibly 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 energy and duration of superflares ($T_{\text{duration }}\propto E^2$) is analyzed. We derive the power-law index to be ${\hat{I}}^2=0.42\pm 0.01$, which is a little larger than ${\hat{I}}^2=1/3$ from the prediction according to magnetic reconnection theory.

Accepted for Publication in ApJ. Comments are welcome. 22 pages, 10 figures, 8 tables