A two-temperature model for the flare of 5 September, 1973

The energetics and mass transfer during the X-ray flare of 18:31 GMT on 5 September, 1973 have been studied using the observations in the objective grating mode of the AS and EX-ray spectrographic telescope on Skylab. The flare was a moderately energetic one, Class M1 according to Solrad. In Hα however, it was only a subflare of class - N. The data are approximately monochromatic images of the small X-ray source. They show a continued rise in the emission for several minutes followed by a decline. The size and temporal evolution are slightly different for ions associated with higher temperatures (Fe XXII, Si XIII) than with those of lower temperatures (Fe XVII, Mg XI). The time of maximum emission moves from one side of the flare to the other and peaks earlier for hotter temperature ions. The observations are analyzed using a two-temperature model in order to determine the changes in the distribution of emission measure and of the amount of material as a function of temperature. The development of the flare can be divided into three periods in each of which different mechanisms are operating. For the first 3-4 min, evaporation drives mass into the entire emitting region. Second, the evaporation ceases: Hot material loses energy, and we see a loss of hot material and a corresponding gain of cool material. Later, after 18:38, we see a decline in the emission measure. (orig.)