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 $\gamma$ of the superflare frequency distribution ($dN/dE\propto E^{-\gamma}$) is constrained to be $\gamma = 2.16\pm 0.10$, 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 ($T_{\text {duration }} \propto E^{\beta}$) is analyzed. We derive the power-law index to be $\beta=0.42\pm0.01$, which is a little larger than $\beta=1/3$ from the prediction according to magnetic reconnection theory.

• The paper reports a higher frequency of superflares on solar-type stars observed by TESS compared to previous Kepler studies, analyzing 1216 superflares on 400 stars.
• Rapidly rotating solar-type stars exhibit a higher incidence of superflares, reinforcing the link between stellar rotation and flare activity.
• The derived energy-duration relation for superflares shows a slight deviation from theoretical predictions, consistent with prior Kepler results and suggesting unique physical processes.

Superflares on Solar-type Stars from TESS Observations

The investigation of superflares on solar-type stars provides significant insights into stellar activities and their potential impacts. The study conducted using the Transiting Exoplanet Survey Satellite (TESS) enriches our understanding of such phenomena. Through a systematic analysis of TESS data from 13 sectors covering 25,734 solar-type stars, this paper identifies 1216 superflares across 400 stars, highlighting captivating differences from prior investigations using Kepler data.

Key Findings and Contributions

1. Higher Superflare Frequency: The frequency of superflares detected by TESS on solar-type stars appears notably higher than that reported using Kepler data. The observed power-law index for superflare frequency distribution, denoted by $\gamma = 2.16 \pm 0.10$, aligns with previous Kepler results, nevertheless suggesting a slightly larger value than typically observed for solar flares. This finding could be attributed to the dominance of young, rapidly rotating stars in the TESS dataset.
2. Rapidly Rotating Stars and Superflare Activity: The study underscores that rapidly rotating solar-type stars exhibit a higher incidence of superflares when compared to their slowly rotating counterparts. This correlation reinforces the notion that stellar rotation plays a critical role in driving superflare activities. The flare frequency inversely related to stellar periods further emphasizes that younger stars are more active flare producers.
3. Energy-Duration Correlation: The derived relation between superflare energy and duration, with a power-law index $\beta=0.42 \pm 0.01$, deviates slightly from the magnetic reconnection theory prediction of $\beta=1/3$. This deviation, consistent with previous studies using Kepler data, suggests potential differences in the underlying physical processes of superflares compared to solar flares.
4. Implications of Potential Hot Jupiters: The study investigates potential planetary companions to the observed flare stars. Although a few flare stars have planet candidates, the absence of a ubiquitous correlation between hot Jupiters and superflares in this dataset indicates that stellar magnetic activities, rather than planet-star interactions, are likely the primary driver of superflares.

Implications and Future Outlook

The implications of these findings are manifold. On a theoretical level, understanding the dynamics of superflares aids in developing comprehensive models of stellar activity and magnetic field interactions. Practically, insights from this study can inform assessments of the potential impacts of superflares on surrounding planetary environments, which is crucial for evaluating conditions conducive to habitability.

The robust dataset furnished by TESS, targeting bright and nearby stars, facilitates extended ground-based follow-up observations. Future research should consider refining periodicity estimations and identifying binary systems to enhance the integrity of the superflare frequency analysis. As TESS continues to explore the northern hemisphere, further observations will provide a more complete picture, potentially augmenting the sample size of Sun-like star superflares and allowing for more definitive statistical conclusions.

In summation, this research contributes valuable knowledge to the field of stellar astrophysics by leveraging TESS data to elucidate the nature and frequency of superflares on solar-type stars. The outcomes further suggest practical approaches and theoretical frameworks for future investigations into stellar activity phenomena and their wide-ranging implications.