Flaring time interval distribution and spatial correlation of major X‐ray solar flares

Abstract

A statistical study is performed on X‐ray flares stronger than C1 class that erupted during the solar maximum between 1989 and 1991. We have investigated the flaring time interval distribution (waiting‐time distribution) and the spatial correlation of successive flare pairs. The observed waiting‐time distribution for the whole data is found to be well represented by a nonstationary Poisson probability function with time‐varying mean flaring rates. The period most suitable for a constant mean flaring rate is determined to be 2–3 days by a Kolmogorov‐Smirnov test. We have also found that the waiting‐time distribution for flares in individual active regions follows a stationary Poisson probability function m exp(− mt ) with a corresponding mean flaring rate. Therefore the flaring probability within a given time is given by 1 ‐ exp(‐ mt ), when the mean flaring rate m is properly estimated. It is also found that there are no systematic relationships between peak fluxes of flares and their waiting‐time distributions. The above findings support the idea that the solar corona is in a self‐organized critical state. A comparison of the angular distances of successively observed flare pairs with those of hypothetical flare pairs generated by random distribution shows a positive angular correlation within ∼ 10° (∼ 180 arc sec in the observing field) of angular separation, which suggests that homologous flares occurring in the same active region should outnumber sympathetic flares.