The extreme-ultraviolet continuum of a strong stellar flare

We present the serendipitous detection of an extreme-ultraviolet flare on EUVE J0613-23.9B. The flare showed over a 200-fold increase above the quiescent emission in the DS/Lexan 60-200 Angstrom wavelength band. Optical spectroscopy revealed that the event was associated with an active dM3.5e star. The EUVE spectra are dominated by emission lines formed at temperatures in excess of 10(7) K. The observation is unique as we have detected, for the first time, a strong Lyman continuum in the EUVE long-wavelength range (320-650 Angstrom). The flare in the continuum (T approximate to 20,000-30,000 K) was extremely short, lasting for less than 500 s, while in the DS (T approximate to 10(7) K) its duration was approximate to28 ks. The total energy of the flare in the DS is similar to3 x 10(34) ergs. We have made a fit to the continuum using semiempirical model atmospheres and derived the time-averaged temperature and density structures.