Close-up of the integrated water maser emission in VLA 3-N (shown in Fig. 2) for the northern (upper panel) and southern (lower panel) bow-shock structures for the first epoch of the VLBA observations on 2001 December 2 (the spatial distribution of the water maser emission is very similar in the two other observed epochs, 2002 February 11 and 2002 March 5). Contours levels are 0.7, 1.2, 2, 4, 10, 20 and 60 Jy beam⁻¹ (beam ≃ 0.45 mas).