Top: Broken power law fit to the 9.0 GHz light curve. Data points are the same as for Fig. 1. The red lines show a random selection of 200 out of 5000 trace samples from the MCMC model fitting. See the corresponding corner plots in Fig. B1. Bottom: Radio spectral index temporal evolution between frequency pairs 9.0/16.7, 9.0/21.2, and 16.7/21.2 GHz. The broken power law model traces of the 9.0 GHz light curve were used to interpolate the 9.0 GHz flux to the time of the 16.7 and 21.2 GHz observations. Filled data points are spectral indices calculated using the detections (SNR ≥ 3) at 16.7 and 21.2 GHz, whereas open circles show the spectral index calculated using the force-fitted flux density values (SNR < 3).