Upper panel: low spectral resolution spectrum spatially averaged over a 0′′.7 × 0′′.7 region centered at α = 20^h29^m24^s.876, δ = +40°11′19′′.216 covering cores A, B, C. Middle panel: zoom-in to the frequency range from 354.2 to 355.3 GHz. Bottom panel: zoom in to the frequency range from 356.4 to 357.1 GHz. The horizontal gray dashed line corresponds to the 5σ signal-to-noise level (σ = 3.4 mJy beam⁻¹).