EUVE Observations of a Rare Impulsive Flare on EV Lac

The M dwarf flare star EV Lac, known for producing extreme flares at both optical and X-ray wavelengths, was observed with EUVE during 1993 Sep 9-13. Most stellar soft X-ray flares are gradual-phase flares, and this has been true also of flares observed with EUVE from AU Mic (Cully \etal 1993, Ap.J. Lett 414, L49), and AD Leo (Hawley \etal 1993, BAAS 25, 856): both had durations > 1 day. EV Lac, however, continued its atypical behavior by producing a rare impulsive flare lasting only about 2 minutes, but with a factor ~ 10 flux increase in the 70 Angstroms - 180 Angstroms passband. It was seen simultaneously in independent detectors (the spectrometers and the Deep Survey instruments), and accounted for a significant fraction of the flux from the entire 100 ksec observation. We derive a density estimate for the flare, and also the emission measure distribution of both the flare and the quiescent corona. Author C.W. Ambruster acknowledges support from NASA grant NAG 5-2279.