Evolution with time of the spectral parameters. Variation of the optical extinction A_V (top) and of the optical spectral index β (centre). Blue stars represent the values obtained by four SEDs as reported in Table 1. The green area refers to the model with A_V fixed, while the orange area to the model with β fixed. The red squares (bottom) represent the variation of the X-ray photon index Γ, which at late times settles around the value ~1.6 ± 0.1 (grey area).