Graffagnino, Vito Giuseppe; (2000) Rosat observations of superflares on RS CVn systems. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The following thesis involves the analysis of a number of X-ray observations of two RS CVn systems, made using the ROSAT satellite. These observations have revealed a number of long-duration flares lasting several days (much longer than previously observed in the X-ray energy band) and emitting energies which total a few percent of the available magnetic energy of the stellar system and thus far greater than previously encountered. Calculations based on the spectrally fitted parameters show that simple flare mechanisms and standard two-ribbon flare models cannot explain the observations satisfactorily and continued heating was observed during the outbursts. This is the first time that such departures from two-ribbon flare models have been identified unambiguously for such large flares, however for some of these outbursts the situation is complicated by the fact that other flaring activity may have been superimposed on the observed lightcurves. By analysing the general decay of the flares, loop heights were derived. Although these loop heights are dependendent on the amount of heating assumed, the calculations were performed for a wide range of reasonable heating values. For these cases the flare heights obtained for these outbursts were of the order of the inter-binary separation and inter-binary flares are suggested as the cause of the outbursts.

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