BVRCIC MONITORING OF ON-231 DURING THE GREAT OUTBURST IN 1994-1997

We present the most continuous data base of optical multiband data eve r published on the BL Lacertae object ON 231 (W Com). The data have be en collected during an intensive and coordinated BVRcIc monitoring cam paign carried out in the period from March 1994 to March 1997. During our campaign, the source brightness was at the highest level ever obse rved. The light curve shows a complex structure, characterized by the presence of three major outbursts having the observed maxima in March 1995, February 1996, and January 1997, when ON 231 reached its histori cal maximum (B similar or equal to 14.2). Variability oil time scales from a few hours up to a month have frequently been observed and the l ight curve seems to be the superposition of many flares with different amplitudes and time scales. The broad-band optical spectral energy di stribution is characterized by a spectral slope which correlates with the flux level. In particular, the higher is the flux the flatter is t he spectrum.