Figure 5

Scatter plot of flare energy as a function of spot area. The lower and upper horizontal axes indicate the area of the starspot group in the unit of the area of the solar hemisphere and the magnetic flux for B=3,000 G. The vertical axis represents the bolometric energy released by each flare. Filled squares and small crosses indicate superflares on G-type main sequence stars detected from short- (this work) and long-cadence data (Shibayama et al. 2013), respectively. Small filled circles represent solar flares (Ishii et al., private communication, based on the data retrieved from the website of the National Geophysical Data Center of the National Oceanic and Atmospheric Administration (NOAA/NGDC), Solar-Terrestrial Physics Division at http://www.ngdc.noaa.gov/stp/). The area of the starspot group for G-type main sequence stars was estimated from the full amplitude of light variations during each observation period in which the flare occurred using Equation 3. We assumed that bolometric energies of B, C, M, X, and X10 class solar flares are 10²⁸, 10²⁹, 10³⁰, 10³¹, and 10³² erg from observational estimates of energies of typical solar flares (e.g., Benz 2008; Emslie et al. 2012).