2009IAUC.9047....2D

R. Decarli and A. Treves, Universita dell'Insubria, Como; R. Falomo, Osservatorio Astronomico di Padova and INAF; M. Dotti, University of Michigan; M. Colpi, Universita di Milano-Bicocca; and J. K. Kotilainen, Tuorla Observatory, University of Turku, report on a deep K-band image taken at the European Southern Observatory of the quasar SDSS J153636.22+044127.0 on Apr. 30.29 UT using the Very Large Telescope (+ HAWK-I). The spectrum of this radio-quiet QSO (z = 0.3893) exhibits two broad emission-line systems at slightly different redshifts (differing by 3300 km/s) in the Sloan Digital Sky Survey optical spectrum and was thus proposed as a candidate binary massive-black-hole system with sub-parsec separation (Boroson and Lauer 2009, Nature 458, 53). The new VLT image shows that the object is composed of two sources (with total magnitudes m_K = 14.1 and 15.8) at a separation of 1" (5.3 kpc). Both sources consist of a nucleus plus an extended emission; the host galaxies, with nuclei components subtracted, have total magnitudes m_K = 15.6 and 16.2. These results strongly suggest that SDSS J1536+0441 is a kpc-scale pair of quasars. This interpretation is consistent with the recent independent finding of two compact radio sources in the same source by Wrobel and Laor (2009, http://lanl.arxiv.org/abs/0905.3566).