The Occurrence Rate of Soft X‐Ray Flares as a Function of Solar Activity

Abstract

In this paper we investigate the occurrence rate of soft X-ray solar flares observed by the Geostationary Operational Environmental Satellites (GOES). The analysis includes all flares classified as equal to or brighter than A1 and covers the time period from 1993 November to 1995 July. We find a power-law relationship between the number of flares per hour and peak X-ray brightness in the 18 Å range. The average power-law index for dN/dF, where N is the number of events per hour and F, the GOES flux, is about -1.88 ± 0.21. A similar result was found from previous work based on uncollimated GOES-typeobservations concerning flares brighter than about C2. This index is independent of the background flux level (which is related to the solar activity level) to within our statistical uncertainties. We obtain the FWHM distribution of flare lifetimes from our sample and find that the distribution is independent of X-ray brightness class. We extrapolate the soft X-ray flare occurrence rate obtained for the Sun to other very active solar-like stars.