Accurate photometric light curves of the lensed components of Q2237+0305 derived with an optimal image subtraction technique: Evidence for microlensing in image A

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août 17, B5c, 4000 Sart Tilman, Belgium e-mail: libbrecht@astro.ulg.ac.be
² ARCSEC, Dept. of Astronomy, Sejong University, Goonja-dong, Kwangjin-gu, Seoul, Republic of Korea

Received: 24 August 2004
Accepted: 3 March 2005

Abstract

Using an optimal image subtraction technique, we have derived the V and R light curves of the four lensed QSO components of Q2237+0305 from the monitoring CCD frames obtained by the GLITP collaboration with the 2.6 m NOT telescope in 1999/2000 (Alcalde et al. 2002). We give here a detailed account of the data reduction and analysis and of the error estimates. In agreement with Woźniak et al. (2000a,b), the good derived photometric accuracy of the GLITP data allows to discuss the possible interpretation of the light curve of component A as due to a microlensing event taking place in the deflecting galaxy. This interpretation is strengthened by the colour dependence of the early rise of the light curve of component A, as it probably corresponds to a caustics crossing by the QSO source.