1997A&A...328..565E

We present two ROSAT-HRI observations of the RS CVn-type binary HU Virginis (=HD 106225). The first observation covers almost three consecutive rotation cycles of HU Virginis or a total of 26.7 days and an exposure time of 35 ksec. On JD 2,449,544 a long duration flare was detected and observed for 1.5 days. This event was releasing a total energy of ≃7.7^+3.3_–1.9x10³⁶erg in the 0.1-2.4keV bandpass. The good coverage of the onset and maximium phase of the flare light curve allowed a detailed comparison with two solar flare models. We derived an estimate for the size of the active region responsible for the flare. The resulting loop size is of the order of one stellar radius. One year later, in 1995, HU Virginis was again observed by ROSAT continuously for 8 days and a total exposure time of 69ksec. The X-ray flux shows variability on time scales shorter than the rotational period.