SIMULTANEOUS DETECTION OF A LARGE FLARE IN THE X-RAY AND OPTICAL REGIONS ON THE RS CVN-TYPE STAR-II PEG

Results are presented for a large flare detected simultaneously on the RS CVn star II Peg by the X-ray satellite GINGA and from ground-based Johnson U-band measurements. We estimate the total U-band flare energy to be at least 6.6 x 10(34) erg. This compares with at least 4.6 x 10(34) erg in the 1-10 keV energy range. These values are lower limits to the true radiative output, since the U-band data relates only to the rise phase of the flare, while the X-ray data were obtained during part of the decay phase. Using a `smooth-burst model', we estimate that the combined U-band plus X-ray radiative output is almost-equal-to 3 x 10(35) erg.