X-Ray Constraints on the Spectral Energy Distribution of the z = 5.18 Blazar SDSS J013127.34-032100.1

Abstract

We report on X-ray measurements constraining the spectral energy distribution (SED) of the high-redshift z = 5.18 blazar SDSS J013127.34-032100.1 with new XMM-Newton and NuSTAR exposures. The blazar's X-ray spectrum is well fit by a power law with Γ = 1.9 and ${N}_{{\rm{H}}}=1.1\times {10}^{21}\,{\mathrm{cm}}^{-2}$ , or a broken power law with ${{\rm{\Gamma }}}_{l}=0.7$ , ${{\rm{\Gamma }}}_{h}=1.8$ , and a break energy ${E}_{b}=0.7\,\mathrm{keV}$ for an expected absorbing column density of ${N}_{{\rm{H}}}=3.6\times {10}^{20}\ {\mathrm{cm}}^{-2}$ , supported by spectral fitting of a nearby bright source. No additional spectral break is found at higher X-ray energies (1-30 keV). We supplement the X-ray data with lower-energy radio-to-optical measurements and Fermi-LAT gamma-ray upper limits, construct broadband SEDs of the source, and model the SEDs using a synchro-Compton scenario. This modeling constrains the bulk Doppler factor of the jets to ≥7 and ≥6 (90%) for the low- and high-N_H SEDs, respectively. The corresponding beaming implies ≥130 (low N_H) or $\geqslant 100$ (high N_H) high-spin supermassive black holes similar to J0131 exist at similar redshifts.