Image collapsed along the spectral axis (left, see Sect. 2), and the corresponding position-angle diagram (right) with the peak positions marked by white squares, and a linear fit to the positions of the first winding. A spiral arm consistent with the fit is plotted on top of the image. A white, dashed part of the spiral is the continuation of the fit. Branches of the windings are marked by the red, dashed line. The flux scale is in Jy beam⁻¹.