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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.62] Observations of Superhot Plasma in Solar Flares

N. Nitta (LMSAL), H. S. Hudson (SPRC)

We have shown in an M1-class flare that a structure away from the main bright loop filled with superhot (\sim30 MK) plasma. The analysis incorporated Yohkoh SXT measurements in three filters and BCS Fe XXV and Ca XIX spectra. We made use of the fact that even the thickest filter of SXT is sensitive to plasma of \sim10 MK, biasing the temperature determination towards lower values. This resulted in an estimated temperature of the imaged superhot plasma consistent with that derived from hard X-rays (the Yohkoh HXT M1/L channel ratio). We now apply the same technique to several other flares to study the existence of superhot plasma, its timing and location with respective to the impulsive component and its range of parameters. We identify flares with superhot plasma irrespective of the results from the BCS Fe XXVI diagnostic (which has large uncertainty), suggesting that the latter should not be the only method to determine whether a flare has superhot plasma. We also discuss the data in terms of the true differential emission measure (a local property of the plasma) rather than the spatial-composite emission measure (the average along the line of sight).

Program listing for Friday