Integral-field spectrophotometry of the quadruple QSO HE 0435-1223: Evidence for microlensingL. Wisotzki, T. Becker, L. Christensen, A. Helms, K. Jahnke, A. Kelz, M. M. Roth and S. F. SanchezA&A, 408 2 (2003) 455-463DOI: https://doi.org/10.1051/0004-6361:20031004