Abstract
Abstract In this paper we present the optical behaviour of Mrk 421 from 1992 to April, 1995. The observations were obtained at the Perugia University Observatory with the automatic imaging telescope in the BVR c I c broad-bands. Visual estimates done by “The Astronomer” group and the British Astronomical Association (BAA) are inclosed in the light curve to give a better temporal coverage. During our monitoring the object showed many flares and major outbursts over a large span of temporal scales. From our data there is also a clear correlation between the colour index and the brightness level, which may be due to the thermal contribution of the host galaxy. Furthermore, we found that the X and TeV flares observed in MrK 421 during 1992–1995 are not well correlated with the more intense optical flares. These data, together with the relative stability of the spectral slope during the optical activity, suggest that the optical emission may be related to knots moving in the jet along a helical path.
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