Radio spectrum of F2. The fluxes were taken from Brentjens (2008), except for the 63 MHz LOFAR flux. The solid line is a second order polynomial fit through the flux density measurements in log (S) − log (ν) space. During the fitting procedure, we assumed 10% uncertainty because the flux density measurements are not all consistent within their 1σ reported errors (plotted in the figure). This prevents the fit to be forced to go through a few measurements with small reported uncertainties.