We report the serendipitous discovery of a flare star observed with the ROSAT X-ray observatory .
From optical spectra , which show strong and variable emission lines of the hydrogen Balmer series and neutral helium , we classify this object as a M3.0Ve star , and estimate a distance of 52 pc from published photometry .
Due to the star ’ s close proximity ( 13.6 ^ { \prime } ) to the calibration source and RS CVn binary AR Lacertae , long term X-ray coverage is available in the ROSAT archive ( \sim 50 hours spanning 6.5 years ) .
Two large flare events occurred early in the mission ( 6-7/1990 ) , and the end of a third flare was detected in 6/1996 .
One flare , observed with the Position Sensitive Proportional Counter ( PSPC ) , had a peak luminosity L _ { X } =1.1 \times 10 ^ { 30 } erg s ^ { -1 } , an e-folding rise time of 2.2 hours and a decay time of 7 hours .
This decay time is one of the longest detected on a dMe star , providing evidence for the possibility of additional heating during the decay phase .
A large HRI flare ( peak L _ { X } =2.9 \times 10 ^ { 30 } erg s ^ { -1 } ) is also studied .
The “ background ” X-ray emission is also variable - evidence for low-level flaring or microflaring .
We find that \geq 59 % of the HRI counts and \geq 68 % of the PSPC counts are due to flares .
At least 41 % of the HRI exposure time and 47 % of the PSPC are affected by detectable flare enhancement .