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.
Categories: astro-ph.GA