Histogram of the radio spectral index using RATAN-600 data from 4.6 GHz to 11.2 GHz during the hypersoft state (blue) and the minor radio flaring state (red). The radio spectrum during the hypersoft state is mostly inverted, optically thick, while in the minor flaring state it is flatter or optically thin. The spectral index during the radio spectrum shown in Fig. 6 is indicated as a dotted line.