Upper panels: sections of the Protostellar Interferometric Line Survey toward a position one beam offset from source B displaying two potential lines of NCN. The model described in Sect. 5 is indicated in red. The E_up values of the two transitions are indicated in green in the upper part of each panel. Lower panel: integrated intensity map of the transition at 322.7878 GHz. The blue contours correspond to 5 and 7σ. The red triangle indicates the position of the continuum peak position, while the red circle indicates the position we analyzed (one beam offset).