Distribution of lifetimes for coronal soft X-ray bright points

Abstract

We have measured the lifetimes of all compact emission features visible on three sets of high time resolution soft X-ray images. The spectrum of lifetimes is found to be heavily weighted toward short lifetimes. The number of features present on the disk which live 2–48 hours is at least ten times as great as the number living more than 48 hours. The distribution of lifetimes can be fit in all three cases by a four-parameter function N(t) = N _s exp(-t/τ _s ) + N _L exp(-t/τ _L ), with τ _s = 8.7±0.2, τ _L = 35±4 and N _s ≈ 10N _L . Features living two days or less have a very broad latitude distribution (Golub et al., 1974, 1975) whereas nearly all longer-lived features are found within 30° of the equator. The growth rates of long-lived vs short-lived points are the same to within ≈ 20%, the major difference being that long-lived points continue to grow and generally reach larger sizes.