Different Power-Law Indices in the Frequency Distributions of Flares with and without Coronal Mass Ejections

Abstract

We investigated the frequency distributions of flares with and without coronal mass ejections (CMEs) as a function of flare parameters (peak flux, fluence, and duration of soft X-ray flares). We used CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission and soft X-ray flares (C3.2 and above) observed by the Geostationary Operational Environmental Satellite (GOES) during 1996-2005. We found that the distributions obey a power law of the form dN/dX~X^-α, where X is a flare parameter and dN is the number of events recorded within the interval [X, X+dX]. For the flares with (without) CMEs, we obtained the power-law index α=1.98+/-0.05 (α=2.52+/-0.03) for the peak flux, α=1.79+/-0.05 (α=2.47+/-0.11) for the fluence, and α=2.49+/-0.11 (α=3.22+/-0.15) for the duration. The power-law indices for flares without CMEs are steeper than those for flares with CMEs. The larger power-law index for flares without CMEs supports the possibility that nanoflares contribute to coronal heating.