Solar flare waiting time distribution: Varying-rate Poisson or Levy function?

The waiting time distribution for solar flares has been considered. Using G eostationary Operational Environmental Satellite X-ray data, we show that a local Poisson hypothesis for solar flares is not consistent with observati ons, while the observed distribution is well reproduced by a Levy function, which displays asymptotically a power-law tail. The origin of the observed waiting time distribution is then attributed to the fact that the physical process underlying solar flares is statistically self-similar in time and is characterized by a certain amount of "memory".