(a) Extent of the H|$_2$|O maser distribution around W Hya against the stellar light curve phase. The vertical broken line indicates the offset phase (⁠|$\Delta \phi \simeq 0.19$|⁠) of the maser flux maximum with respect to the optical light curve maximum, which is derived by Shintani et al. (2008). (b) Same as panel (a) but the vertical scale shows the peak flux density of the maser in the synthesized image cube.