Only very few z > 5 quasars discovered to date are radio-loud , with a radio-to-optical flux ratio ( radio-loudness parameter ) higher than 10 .
Here we report the discovery of an optically luminous radio-loud quasar , SDSS J013127.34 - 032100.1 ( J0131 - 0321 in short ) , at z = 5.18 \pm 0.01 using the Lijiang 2.4m and Magellan telescopes .
J0131 - 0321 has a spectral energy distribution consistent with that of radio-loud quasars .
With an i -band magnitude of 18.47 and radio flux density of 33 mJy , its radio-loudness parameter is \sim 100 .
The optical and near-infrared spectra taken by Magellan enable us to estimate its bolometric luminosity to be L _ { bol } \sim 1.1 \times 10 ^ { 48 } erg s ^ { -1 } , approximately 4.5 times greater than that of the most distant quasar known to date .
The black hole mass of J0131 - 0321 is estimated to be 2.7 \times 10 ^ { 9 } M _ { \odot } , with an uncertainty up to 0.4 dex .
Detailed physical properties of this high-redshift , radio-loud , potentially super-Eddington quasar can be probed in the future with more dedicated and intensive follow-up observations using multi-wavelength facilities .