The optical and radio spectrum of the radio-selected high redshift quasar S4 1745+624

The optical and radio spectrum as well as direct imaging data for the strong radio source S4 1745+624, a high redshift quasar with z = 3.886, are presented. The optical continuum redward of Lyman α is rather steep with a spectral index of α = −1.3 and the continuum depression blueward of the Lyman α λ1216 emission line is smaller than in optically selected quasars of similar redshift. The overall radio spectrum differs markedly from that of other high redshift radio quasars, showing a steep low frequency part and a flat high frequency part