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 highredshift 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 H = 1.1 × 10 21 cm −2 , or a broken power law with Γ l = 0.5, Γ h = 1.8, and a break energy E b = 0.7 keV for an expected absorbing column density of N H = 3.6 × 10 20 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 ≥100 (high N H ) high-spin supermassive black holes similar to J0131 exist at similar redshifts.

Chandra Detection of Three X-ray Bright Quasars at z>5

“…The observed 0.5 − 2 keV flux of J074749+115352 is F 0.5−2keV = 3.49 +0.44 −0.45 × 10 −14 erg s −1 cm −2 . To our knowledge, this is the X-ray brightest radio quiet quasar at z > 5, only after two radio loud blazars [Q0906+6930 at z = 5.48, Romani (2006); SDSS J013127.34-032100.1 at z = 5.18, An & Romani (2020)] and a radio loud non-blazar quasar CFHQS J142952+544717 at z = 6.18 recently detected in X-ray by Medvedev et al (2020) with eROSITA (the X-ray brightest quasar at z > 5, with an observed 0.3 − 2 keV Å is the monochromatic luminosity at 2500 Å, and is computed from M 1450 assuming a power law spectral index of α = −0.5 in UV band. N H is the Galactic foreground absorption column density toward the quasar obtained from the HEASARC webtools using the HI4PI full-sky H I map (HI4PI Collaboration 2016).…”