2021MNRAS.503.4662M

We report the first detection at 4.7 and 8.2 GHz with the RATAN-600 radio telescope of the source PSO J047.4478+27.2992, which has been announced as a blazar at z = 6.1. The average flux densities are 12 ± 3 and 8 ± 4 mJy at 4.7 and 8.2 GHz respectively, and an upper limit is estimated as 3 mJy at 11.2 GHz. The light curve at 4.7 GHz, obtained on a time-scale of four months, exhibits moderate variability of the source (fractional variability F_var = 0.28 ± 0.02). The new RATAN-600 measurements extend previous literature data to higher frequencies, indicating a single power-law radio spectrum with α_0.147–8.2 = -0.51 ± 0.1. The monochromatic radio luminosity at 4.7 GHz P_ν ∼ 2 x 10²⁷ W Hz^–1 is consistent with values for high-redshift quasars at z >= 3.