Radio Identification of the X-Ray Jet in the z =4.3 Quasar GB 1508+5714

The recent discovery of an X-ray jet in the z = 4.3 quasar GB 1508+5714 by Yuan et al. and Siemiginowska et al. prompted a search for its radio counterpart. Here, we report the successful discovery of faint radio emission from the jet at 1.4 GHz using archival Very Large Array data. The X-ray emission is best interpreted as inverse Compton (IC) emission off the cosmic microwave background (CMB) as discussed by the previous investigators. In this scenario, its high X-ray-to-radio monochromatic luminosity ratio, compared to previously detected IC/CMB X-ray jets at lower redshift, is a natural consequence of its high redshift.