The Optical Gravitational Lensing Experiment Monitoring of QSO 2237+0305

Abstract

We present results from 2 yr of monitoring of Huchra's lens (QSO 2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry in the V band was done using a newly developed method for image subtraction. Reliable subtraction without Fourier division removes all complexities associated with the presence of a bright lensing galaxy. With the positions of the lensed images adopted from Hubble Space Telescope (HST) measurements, it is relatively easy to fit the variable part of the flux in this system, as opposed to modeling the underlying galaxy. For the first time, we observed smooth light variation over a period of a few months, which can be naturally attributed to microlensing. We also describe automated software capable of real-time analysis of the images of QSO 2237+0305. It is expected that starting from the next observing season in 1999, an alert system will be implemented for high-amplification events in this object. The time sampling and photometric accuracy achieved should be sufficient for early detection of caustic crossings.

Based on observations obtained with the 1.3 m Warsaw telescope at the Las Campanas Observatory of the Carnegie Institution of Washington.