Interpretation of the OGLE Q2237 0305 microlensing light curve (1997-1999)

Abstract

The four bright images of the gravitationally lensed quasar Q2237+ 0305 are being monitored from the ground (e.g. OGLE collaboration, Apache Point Observatory) in the hope of observing a high-magnification event (HME). Over the past three seasons (1997-1999) the OGLE collaboration has produced microlensing light curves with unprecedented coverage. These demonstrate smooth, independent (therefore microlensing) variability between the images. We have retrospectively applied probability functions for HME parameters to the observed light-curve features. We conclude that the 1999 image C peak was as a result of the source having passed outside of a cusp rather than to a caustic crossing. In addit..