Statistical properties of superflares on solar-type stars based on 1-min cadence data

TL;DR

This study analyzes superflares on solar-type stars using high-cadence Kepler data, revealing their frequency, energy distribution, and temporal properties, and compares these with solar flares to understand their magnetic origins.

Contribution

It provides the first detailed analysis of superflares with 1-minute cadence data, establishing their power-law energy distribution and relation between flare energy and duration.

Findings

Superflares with energies up to 10^{36} erg were detected on 23 stars.

The occurrence frequency follows a power-law distribution with index approximately -1.5.

Flares' duration scales with energy as τ ∝ E^{0.39}, consistent with Alfvén timescales.

Abstract

We searched for superflares on solar-type stars using Kepler data with 1 min sampling in order to detect superflares with short duration. We found 187 superflares on 23 solar-type stars whose bolometric energy ranges from the order of $10^{32}$ erg to $10^{36}$ erg. Some superflares show multiple peaks with the peak separation of the order of $100$-$1000$ seconds which is comparable to the periods of quasi-periodic pulsations in solar and stellar flares. Using these new data combined with the results from the data with 30 min sampling, we found the occurrence frequency ($dN/dE$) of superflares as a function of flare energy ($E$) shows the power-law distribution ($dN/dE \propto E^{-\alpha}$) with $\alpha \sim -1.5$ for $10^{33}<E<10^{36}$ erg which is consistent with the previous results. The average occurrence rate of superflares with the energy of $10^{33}$ erg which is equivalent to X100 solar flares is about once in 500-600 years. The upper limit of energy released by superflares is basically comparable to a fraction of the magnetic energy stored near starspots which is estimated from the photometry. We also found that the duration of superflares ($\tau$) increases with the flare energy ($E$) as $\tau \propto E^{0.39\pm 0.03}$. This can be explained if we assume the time-scale of flares is determined by the Alfv$\acute{\rm e}$n time.