QSO 2237+0305 photometry and light curves

We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0m Liverpool Telescope and the 1.5m Maidanak Telescope. These gVrRI frames over the 2006-2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A-D. Through difference light curves, we found strong microlensing signatures.

We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: R_{lambda}_{prop.to}{lambda}^{alpha}^, {alpha}=1.33+/-0.09.