Temporal Variation of Flare Occurrence Rates via the Spot Evolution on the Sun and Solar-type Stars

Abstract

The spot evolution on the Sun and solar-type stars is important for understanding the nature of consequential flaring activity. This study statistically investigates the variance of flare occurrence rate through the time evolution of spots on the Sun and solar-type stars. We have compiled the 28-year catalogs of solar flares and their source sunspots obtained from solar surface observations by NOAA and GOES for the Sun. Also, we combined the cataloged stellar flares with the time evolution of starspots estimated by light curves obtained by the 4-year Kepler mission for solar-type stars. For the obtained 24124 solar flares and 180 stellar flares, we calculate the flare occurrence distribution with respect to $t_{\mathrm{flare}}-t_{\max }$, which represents the timing of flare through the spot evolution, where $t_{\mathrm{flare}}$ is the flare occurrence time, and $t_{\max }$ is the time when the source spot takes its maximum area. When normalized by the spot lifetime, we found that the flare occurrence distribution for $t_{\mathrm{flare}}-t_{\max }$ shows a similar distribution regardless of spot size or flare energy, suggesting that the Sun and the solar-type star share the same physical process in the spot-to-flare activity. On this basis, we propose a formula for the time variation of the flare occurrence rate per spot. Also, the correlation between the temporal variation of flare occurrence rate and the time evolution of spot area and the lack of difference in flare occurrence rate between the emergence and decaying phases provide a milestone for the nature of flare-productive spots.

21 pages, 12 figures, 2 tables. Accepted for publication in The Astrophysical Journal

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