Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar
  ($z$=6.44)
  We report the 888 MHz radio detection in the Rapid ASKAP Continuum Survey
(RACS) of VIK J2318$-$3113, a $z$=6.44 quasar. Its radio luminosity (1.2
$\times 10^{26}$ W Hz$^{-1}$ at 5 GHz) compared to the optical luminosity (1.8
$\times 10^{24}$ W Hz$^{-1}$ at 4400 A) makes it the most distant radio-loud
quasar observed so far, with a radio loudness R$\sim$70
(R$=L_\mathrm{{5GHz}}/L_\mathrm{{4400A}}$). Moreover, the high bolometric
luminosity of the source (L$_\mathrm{{bol}}$=7.4 $\times 10^{46}$ erg s$^{-1}$)
suggests the presence of a supermassive black hole with a high mass ($\gtrsim$6
$\times$10$^8$ M$_\odot$) at a time when the Universe was younger than a
billion years. Combining the new radio data from RACS with previous ASKAP
observations at the same frequency, we found that the flux density of the
source may have varied by a factor of $\sim$2, which could suggest the presence
of a relativistic jet oriented towards the line of sight, that is, a blazar
nature. However, currently available radio data do not allow us to firmly
characterise the orientation of the source. Further radio and X-ray
observations are needed.
