ROSAT-DETECTION OF A GIANT X-RAY FLARE ON LKH-ALPHA-92

We report the detection of a giant X-ray flare on the classical T Taur i star LkH alpha 92 with the ROSAT PSPC. In this flare the PSPC count rate rose by a factor of more than 100 in a time interval of about 200 0 sec. Our X-ray observations cover most of the rise phase as well as part of the decay phase of the flare. We model the X-ray spectra obtai ned at different flare phases to determine temperature and emission me asure of the flaring plasma. Combining the thus derived X-ray luminosi ty with the observed decay time scale of approximate to 7800 sec, we e stimate the total energy release of the flare in the ROSAT PSPC band ( 0.1 - 2.4 keV) to be approximate to 4 x 10(36) erg, which is more than a factor of 10(4) greater than the energy release in the strongest so lar flares and still more than a factor of 100 greater than that in ty pical flares on T Tauri stars.