SED Constraints on the Highest-z Blazar Jet: QSO J0906+6930

Abstract

We report on Gemini, NuSTAR , and eight years of Fermi observations of the most distant blazar QSO J0906+6930 ( z = 5.48). We construct a broadband spectral energy distribution (SED) and model the SED using a synchro-Compton model. The measurements yield a mass of ∼4 × 10 9 M ⊙ for the black hole and a spectral break at ∼4 keV in the combined fit of the new NuSTAR and archival Chandra data. The SED fitting constrains the bulk Doppler factor δ of the jet to 9 +2.5 −3 for QSO J0906+6930. Similar, but weaker, constraints on δ are derived from SED modeling of the three other claimed z  > 5 blazars. Together, these extrapolate to ∼620 similar sources, fully 20% of the optically bright, high-mass active galactic nuclei expected at 5 <  z  < 5.5. This has interesting implications for the early growth of massive black holes.