5-YEAR PHOTOMETRY OF V635 CASSIOPEIAE - THE OPTICAL COUNTERPART OF 4U0115+63

We report on the results of V, R, I photometry of V635 Cas - the optical counterpart of the X-ray source 4U0115 + 63, during the years 1985-90. Throughout this period three large optical eruptions were detected, two of which were accompanied by an X-ray outburst. The X-ray activity appeared a few hundred days after the onset of the optical outburst. We suggest that the optical eruptions are generated by an accretion disc around the neutron star. We further suggest that the X-ray delay is due to a centrifugal barrier at the neutron star magnetosphere boundary. This effect might be also responsible for the appearance of an optical outburst without any observable X-ray counterpart.