* Astronomy

Title: I. Flux and colour variations of the quadruply imaged quasar HE 0435--1223
Authors: D. Ricci, J. Poels, A. Elyiv, F. Finet, P. G. Sprimont, T. Anguita, V. Bozza, P. Browne, M. Burgdorf, S. Calchi Novati, M. Dominik, S. Dreizler, M. Glitrup, F. Grundahl, K. Harpsøe, F. Hessman, T. C. Hinse, A. Hornstrup, M. Hundertmark, U. G. Jørgensen, C. Liebig, G. Maier, L. Mancini, G. Masi, M. Mathiasen, S. Rahvar, G. Scarpetta J. Skottfelt, C. Snodgrass, J. Southworth, J. Teuber, C. C. Thöne, J. Wambsganß, F. Zimmer, M. Zub, J. Surdej

aims: We present VRi photometric observations of the quadruply imaged quasar HE 0435--1223, carried out with the Danish 1.54 meter telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colours of each lensed component as a function of time.
Methods: We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and PSF (Point Spread Function) fitting.
Results: Between these two seasons, our results show an evident decrease in flux by ~0.2--0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase (~0.05--0.015) in their V-R and R-i colour indices. Conclusions: These flux and colour variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest "A" lensed component.

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