ISOobservations of the dusty quasar BR 1202−0725

We present mid- and far-infrared photometry of the high-redshift (z = 4.69) dusty quasar BR 1202−0725. The quasar was detected in the near-infrared, at a flux level (0.7 ± 0.2 mJy) consistent with an average radio-quiet quasar at its redshift. Only upper limits for the emission were obtained in the far-infrared. These upper limits, when combined with data from ground-based telescopes, are the first direct evidence for a turnover in the far-infrared emission, and hence confirm that a blackbody dominates the spectral energy distribution at far-infrared wavelengths. This blackbody is most probably cool dust, constrained to have a temperature below 80 K, for a β of 1.5.