Monitoring of the Einstein cross with the Nordic optical telescope

: Ostensen R, Refsdal S, Stabell R, Teuber J, Emanuelsen PI, Festin L, FlorentinNielsen R, Gahm G, Gullbring E, Grundahl F, Hjorth J, Jablonski M, Jaunsen AO, Kaas AA, Karttunen H, Kotilainen J, Laurikainen E, Lindgren H, Mahonen P, Nilsson K, Olofsson G, Olsen O, Pettersen BR, Piirola V, Sorensen AN, Takalo L, Thomsen B, Valtaoja E, Vestergaard M, Vianborg TA

Publisher: EDP SCIENCES S A

: 1996

ASTRONOMY & ASTROPHYSICS

: ASTRON ASTROPHYS

: 309

: 1

: 59

: 64

: 6

: 0004-6361

We report results from five years of monitoring of the Einstein Cross (QSO 2237+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.