Fig. 2: SED and radio light curves of J0410−0139.
a, Rest-frame SED from radio to X-rays, showing only the simultaneous VLA 2021 observations. Strong absorption in the UV (shown as 3σ upper limits) is due to absorption from the neutral intergalactic medium at z ≈ 7. The X-ray uncertainties consider 2σ variation in the X-ray photon index and flux densities. The shaded orange regions span the 1σ and 2σ SED distributions for low-redshift flat-spectrum radio blazars16 with similar X-ray luminosities. The orange curve marks the median SED. The grey shading represents the 1σ and 2σ expected X-ray luminosity for a radio-quiet quasar with the same L2,500 (ref. 71). b, Radio SED with data points colour-coded by year (Table 1). The quasar shows strong variability across radio frequencies. Diamonds (squares) represent quasi-simultaneous VLA 2021 (2022) observations, within 15 min in the rest frame. Dashed lines are power-law extrapolations from these measurements. c, Observed 1.4 and 3.0 GHz radio light curves (νobs) (11.2 and 23.9 GHz rest-frame radio light curves, νrest). Data points are normalized to the initial flux density for each frequency, with 1σ error bars shown. The 1.4 GHz values were corrected using spectral index values of α = 0.85 (pre-2022) and α = 0.21 (post-2022).
