Averaged flux density as a function of frequency for all light curves for the time period between 7 h and 11 h UT. The error bars denote measurement error convolved with flux density variability over the track, where variability is the dominant contribution. Variability is strongest at the highest frequencies. The spectral index obtained from using VLA + ALMA data is indicated by the black line (with 1sigma fit uncertainties filled in with gray) and yields α = 0.42 ± 0.03. Using the VLA data only (red/gray line, with red/light gray 1sigma uncertainty region), α = 0.45 ± 0.07.