We present Keck high-resolution near-IR ( 2.2 \mu m ; FWHM \sim 0 \farcs 15 ) and mid-IR ( 12.5 \mu m ; FWHM \sim 0 \farcs 4 ) images of APM 08279+5255 , a z = 3.91 IR-luminous BALQSO with a prodigious apparent bolometric luminosity of 5 \times 10 ^ { 15 } { L } _ { \odot } , the largest known in the universe .
The K -band image shows that this system consists of three components , all of which are likely to be the gravitationally lensed images of the same background object , and the 12.5 \mu m image shows a morphology consistent with such an image configuration .
Our lens model suggests that the magnification factor is \sim 100 from the restframe UV to mid-IR , where most of the luminosity is released .
The intrinsic bolometric luminosity and IR luminosity of APM 08279+5255 are estimated to be 5 \times 10 ^ { 13 } { L } _ { \odot } and 1 \times 10 ^ { 13 } { L } _ { \odot } , respectively .
This indicates that APM 08279+5255 is intriniscally luminous , but it is not the most luminous object known .
As for its dust contents , little can be determined with the currently available data due to the uncertainties associated with the dust emissivity and the possible effects of differential magnification .
We also suggest that the lensing galaxy is likely to be a massive galaxy at z \sim 3 .