Quasi-simultaneous broad-band radio continuum spectra obtained with the Effelsberg 100 m telescope. The spectral index α resulting from a power-law fit is indicated in each panel together with the time of observation. The measurement errors are comparable to or smaller than the symbol size. We note that up to MJD 56 017.2 the spectral index is flat with an average of −0.10 ± 0.02 (see text).