1998A&A...339L..77L

We report observations of the z=3.87 broad absorption line quasar APM 08279+5255 (Irwin et al., 1998ApJ...505..529I) with the Adaptive Optics Bonnette (AOB) of the Canada-France-Hawaii Telescope. The object is found to be a double source. The separation of the two images is 0.35"±0.02" and the intensity ratio I_north/I_south=1.21±0.25 in the H-band. No other image is detected down to H(5σ)=21.3 within 10" from the double image. Strong support for the lensing hypothesis comes from the uniformity of the quasar spectrum as a function of spatial position in the image obtained with the integral field spectrograph OASIS at CFHT. From the 2D-spectroscopy, narrow-band images are reconstructed over the wavelength range 5600-6200Å to search for emission-line objects in a field of 15"x12" around the quasar. We find no such object to a limit of 6x10^–17erg/cm²/s. We use the images centered on the deepest absorption lines of the Lyα forest to dim the quasar and to increase the sensitivity closer to the line of sight. One of the images, centered at 5766.4Å, exhibits a 3σ excess 1.5" from the quasar to the north-east.