Definition of the normals (black lines) to the possible emitting regions by observing the illumination conditions of Fig. 6 at different local times. The color scale refers to the cosine of the solar incidence. Panel A: emitting region on the neck at 4:35 h (peak illumination), see panel A of Fig. 8. Panel B: another possible emitting region (in the head of the comet) at 6:16 h. Panel C: bottom region at 6:56 h. By observing the normal directions and comparing them with the emission of Fig. 2, the emitting region of panel A seems to be a more likely candidate.