Extended X - ray emission in the high redshift quasar GB 1508 + 5714

We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z=4.3, revealed in a long Chandra ACIS observation. The emission feature is 3–4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92 ± 0.35 (90 per cent c.l.). The X-ray flux and luminosity reach 9.2 10 −15 erg cm −2 s −1 (0.5–8 keV) and 1.6 10 45 erg s −1 (2.7–42.4 keV rest frame, Ω Λ =0.73, Ω m =0.27, H 0 =71 km s −1 Mpc −1), which is about 2 percent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of Cosmic Microwave Background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high redshift radio galaxies and quasars, demonstrating that significant power is injected into their surrounding by powerful jets.