P15	March 1998

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² URA 173 CNRS-DAEC, Observatoire de Paris, F-92195 Meudon Principal Cédex, France
³ ESO, Casilla 19001, Santiago 19, Chile
⁴ Institute of theoretical Astrophysics, University of Oslo, Pb. 1029 Blindern, N-0315 Oslo, Norway
⁵ Center for Advanced Study, Drammensvn. 78, N-0271, Norway
⁶ NORDITA, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark
⁷ Department of Physics, University of thromsø, Norway
⁸ Nordic Optical Telescope, Apartado 474, E-38700 St. Cruz de La Palma, Canary Islands, Spain
⁹ ESO, Karl-Schwarzschild-Strasse 2, D-85748, Garching bei München, Germany
¹⁰ Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany

^* Maître de Recherches FNRS, Belgium

⁺ Based on observations obtained at NOT and ESO La Silla

Abstract

     We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3.1", it is the quadruply imaged QSO with the widest known angular separation. Raw and deconvolved data reveal an elongated lens galaxy. The observed reddening in at least two of the four QSO images suggests differential extinction by this lensing galaxy. We show that both an ellipticity of the galaxy _min = 0.075) and an external shear _min = 0.15) from a nearby mass has to be included in the lensing potential in order to reproduce the complex geometry observed in RX J0911.4+0551. A possible galaxy cluster is detected about 38" from RX J0911.4+0551 and could contribute to the X-ray emission observed by ROSAT in this field. The color of these galaxies indicates a plausible redshift in the range of 0.6-0.8.