The decay of the 1973 August 9 flare

Abstract

The state and evolution of the decay-phase plasma from a compact solar flare that occurred on August 9, 1973, are investigated on the basis of XUV and X-ray observations from Skylab and Solrad 9. Density-sensitive line ratios are used to determine the electron density over the temperature range from 30,000 to 5 million K, and the differential emission measure in the temperature interval from 30,000 to 20 million K is derived for several times in the decay phase. The morphology of the flare is discussed, including its relation to the observed photospheric magnetic field. The sequential formation of new loops during the decay phase is emphasized as an essential element for understanding the decay phase of the flare. This idea is developed further by comparing the observed differential emission measure with that predicted by a semiempirical model which considers the sequential formation of isothermal loops that cool by radiation and thermal conduction.