Kavli Affiliate: Roger W. Romani
| First 5 Authors: Hongjun An, Roger W. Romani, , ,
| Summary:
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 $Gamma=1.9$ and $N_{rm H}=1.1times10^{21}rm cm^{-2}$, or a
broken power law with $Gamma_l=0.5$, $Gamma_h=1.8$, and a break energy
$E_b=0.7$ keV for an expected absorbing column density of $N_{rm H}=3.6times
10^{20}rm cm^{-2}$, 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 $ge$7 and $ge$6 (90%) for the low- and
high-$N_{rm H}$ SEDs, respectively. The corresponding beaming implies $ge$130
(low $N_{rm H}$) or $ge$100 (high $N_{rm H}$) high-spin supermassive black
holes similar to J0131 exist at similar redshifts.
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