Relationship between impulsive and post-eruptive processes in solar X-ray flares

Abstract

Powerful solar flares contain one or more impulsive events, plasma ejection, and the subsequent development of gigant post-eruptive loops. In the middle of the 1980s, Jakimiec proposed an analysis of the flare loops based on log T-1/2log EM diagrams constructed from the observed soft X-rays (the so-called Jakimiec model). We have used this method to construct and analyze these diagrams not for various arbitrary events, but instead for similar flares within a single center of activity; in other words, for homological flares (two-ribbon flares observed in November 2000, powerful prolonged events observed in October–November 2003, etc.). This eliminated the effect of differences in the magnetic configurations, enabling us to find a new relationship: the slope (tan α) of the logT-1/2log EM line during the flare decay depends on the maximum temperature Tmax at the source of the soft X-rays. The dependence of tan α on Tmax gradually evolves from a series of short flares to a series of powerful, prolonged, nonstationary processes. Our results support the idea that the development of post-eruptive loops depends on the energy of the impulsive events for the phenomenon as a whole. Explosive evaporation simultaneously increases both the temperature and the density of the plasma at the loop top. The subsequent evolution of the post-eruptive formations depends on the difference in the initial conditions and on the degree of opening of the magnetic configuration. The importance of our analysis for the duration of flares and differences between dimmings is briefly discussed.