VRI PHOTOMETRY OF THE EINSTEIN-CROSS Q2237+0305 AT MAIDANAK OBSERVATORY

Observations of the gravitationally lensed quasar Q2237+0305 were made with tile 1.5-meter AZT-22 telescope at Maidanak (Uzbekistan) on 17-1 9 September 1995. All four components of the quasar are clearly resolv ed. The results of photometric measurements of the components are pres ented. It is confirmed that tile component A again became the brightes t one in the system. A noticeable change of the mutual colours of the components A and B in comparison with previous observations is detecte d and discussed. We cannot decide, oil the basis of existing observati onal data, whether varying extinction or ''chromatic'' microlensing is the cause. Stronger, correlated colour changes in the system are prob ably caused by quasar variability. The dominant time scale of the micr olensing-governed brightness variations since the discovery is of the order of 10 years. A correlation between radio brightness and optical colour is found but cannot be explained.