Left panel: the spectra of NH₃ (9,6) maser transition detected toward W51-IRS2 using TMRT from 2020 January 8 to April 7, which was taken from Zhang et al. (2022). Upper-right panel: the spectra of NH₃ (9,6) maser transition extracted from W51-IRS2, W51-North, and W51d2 regions detected with the VLA. The red dashed lines at ∼54.2 km s⁻¹ in the left and upper-right panels mark the strongest velocity component in the W51d2 subregion. Lower-right panel: the spatial distribution of H₂O maser spots in the whole region of W51-IRS2.