Probing the Nature of the Massive Black Hole Binary Candidate Sdss J1536+0441

We present an imaging study of the black hole binary candidate SDSS J1536+0441 (z ≈ 0.3893), based on deep, high resolution VzK images collected at the ESO/VLT. The images clearly show an asymmetric elongation, indicating the presence of a companion source at ∼ 1 (≈ 5 kpc projected distance) East from the quasar. The host galaxy of the quasar is marginally resolved. We find that the companion source is a luminous galaxy, the light profile of which suggests the presence of an unresolved, faint nucleus (either an obscured AGN or a compact stellar bulge). The study of the environment around the quasar indicates the occurrence of a significant over-density of galaxies with a redshift compatible with z ≈ 0.4. This suggests that it resides in a moderately rich cluster of galaxies. Subject headings: quasars: individual (SDSS J153636.22+044127.0)