We report observations of the z = 3.87 broad absorption line quasar APM 08279+5255 ( Irwin et al .
1998 ) 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 \aas@@fstack { \prime \prime } 35 \pm 0 \aas@@fstack { \prime \prime } 02 and the intensity ratio I _ { north } / I _ { south } = 1.21 \pm 0.25 in the H -band .
No other image is detected down to H ( 5 \sigma ) = 21.3 within 10 \arcsec 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 5600-6200 Å to search for emission-line objects in a field of 15 \arcsec \times 12 \arcsec around the quasar .
We find no such object to a limit of 6 \times 10 ^ { -17 } erg cm ^ { -2 } s ^ { -1 } .
We use the images centered on the deepest absorption lines of the Ly \alpha forest to dim the quasar and to increase the sensitivity closer to the line of sight .
One of the images , centered at 5766.4 Å , exhibits a 3 \sigma excess 1.5 \arcsec from the quasar to the north-east .