NIR to X-ray SED of GRB 161219B at t − t₀ = 0.26,1.47 and 2.55 days. Left: best-fitting model consisting of a broken power-law and MW extinction curve. For all three epochs, we find: β_opt ≈ 0.45, β_X ≈ 0.95 and a break frequency of ν_B ≈ 1.7 − 1.8 × 10¹⁵ Hz. The local reddening is low (E(B − V) ≈ 0.02 mag). Right: to the SED at + 0.26 days, we fit an extinguished broken power-law with an additional blackbody component. At this early epoch (≈+5.4 h, rest-frame), the BB component is very hot (T_BB ≈ 0.16 × 10⁶ K) and it contributes ≈68% of the total recorded flux. (Note that the BB fit implies a larger local reddening than the BPL fits − see the main text for further discussion).