The colour of the narrow line Sy1-blazar 0324+3410

Aims. We investigate the properties of the host galaxy of the blazar J0324+3410 (B2 0321+33) by the analysis of B and R images obtained with the NOT under good photometric conditions. Methods: The galaxy was studied using different methods: Sersic model fitting, unsharp-masked images, B-R image and B-R profile analysis. Results: The images show that the host galaxy has a ring-like morphology. The B-R colour image reveals two bluish zones: one that coincides with the nuclear region, interpreted as the signature of emission related to the active nucleus, the other zone is extended and is located in the host ring-structure. We discuss the hypothesis that the later is thermal emission from a burst of star formation triggered by an interacting/merging process.