Linear polarisation in the 57 km s^-1 component of the (9, 6) maser line on April 5 and 7, 2012. Shown are the two orthogonal components. The left panels display the horizontal (approximately east-west) and the right panels the vertical (approximately north-south) component, because the line was observed close to transit. Since the line is strong, the difference is highly significant and is visible in each of the 20 (April 5) and 60 (April 7) individual subscans. For beam size and channel spacing, see Table 1.