Abstract

In astrophysics, the emitted radiation is usually the only source of iformation about the physical conditions in the emitting medium. Physical properties of the emitting plasma are then derived by analysis and modeling of the observed spectra. For a long time, this has been done under the assumption of a local, equilibrium Maxwellian distribution. We report on the SDO /AIA and Hinode/EIS EUV observations of a transient coronal loop. EIS captures this loop during its brightening phase as observed in most of the AIA filters. We use the AIA data to study the evolution of the loop, as well as to perform the DEM diagnostics as a function of the non-Maxwellian parameter kappa. Fe XI-XIII lines observed by EIS are used to perform the diagnostics of electron density and subsequently the diagnostics of kappa. Using ratios involving the Fe XI 257 .772A selfblend, we diagnose an extreme non-Maxwellian situation with kappa < 2. Using the predicted Fe line intensities derived from the DEMs as a function of kappa, we show that, with decreasing kappa, all combinations of ratios of line intensities converge to the observed values, confirming the diagnosed kappa < 2. These results represent the first positive diagnostics of kappa-distributions in the solar corona despite the limitations imposed by calibration uncertainties.