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 alpha is rather steep with a spectral index of alpha = - 1.3 and the continuum depression blueward of the Lyman alpha lambda1216 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.