On the physics of a long decay X-ray event

A long decay X-ray event (LDE) which appeared as an expanding loop system on the solar limb on 13–14 August 1973 was well observed temporally (with Skylab ATM S056 and S054 X-ray telescopes) and spectrally (with S082A XUV spectroheliograph). We summarize and supplement the extensive discussion in the literature. In addition, a one-dimensional hydrodynamic study is undertaken to investigate both increasing and decreasing phases of the event. Results indicate that the inferred temperature gradients along the loops during the heating phase are consistent with unrestricted dynamic and conductive flows along magnetic field lines. Furthermore, we conclude that it cannot be unequivocally stated that enhanced emission at the tops of loops is due to pressure gradients along the field lines. Finally, the large emission measure variations in the 10⁵–10⁶ K plasma during the event's decline may be due simply to the temperature dependence of radiative decay within a multi-loop configuration.Presently a NRC Associate at NASA/MSFC, Space Sciences Laboratory, MSFC, Ala. 35812, U.S.A.Presently at NASA/MSFC, Space Sciences Laboratory, MSFC, Ala. 35812, U.S.A.