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 Å 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 Å). The flare in the continuum ( T ≈ 20,000-30,000 K) was extremely short, lasting for less than 500 s, while in the DS ( T ≈ 10 7 K) its duration was ≈28 ks. The total energy of the flare in the DS is ~3 × 10 34 ergs. We have made a fit to the continuum using semiempirical model atmospheres and derived the time-averaged temperature and density structures.