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Monitoring of the Einstein Cross with the Nordic Optical Telescope

This paper is available in a repository.
This paper is available in a repository.

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Abstract

. We report results from five years of monitoring of the Einstein Cross (QSO2237+0305) with the Nordic Optical Telescope. The photometry, mainly in the R and I bands, has been performed by a PSF fitting and 'cleaning' procedure, in which the four image components as well as the host galaxy and its nucleus are iteratively removed. The resulting lightcurves exhibit several microlensing features; one event may have a timescale as short as 14 days. Variations on timescales of several years are found in all four images. This becomes even more convincing when our data are combined with data published for 1986-89. No clear high amplification event was observed during the period. A brightening of all four components during 1994 is interpreted as intrinsic variation. Key words: gravitational lenses -- image processing -- PSF photometry -- QSO 2237+0305 1. Introduction After some preliminary observations in 1990, a program was started in 1991 at the Nordic Optical Telescope (NOT) on the island ...