SDSS J013127.34$-$032100.1: A newly discovered radio-loud quasar at
  $z=5.18$ with extremely high luminosity
  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+-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 ~100. The
optical and near-infrared spectra taken by Magellan enable us to estimate its
bolometric luminosity to be L_bol ~ 1.1E48 erg/s, 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 2.7E9 solar masses, 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.
