Spectrum of the water maser detected by Pesce et al. (2015) with the Green Bank Telescope, where we report the velocity coverage (1400 km s⁻¹) of the two IFs used during the VLBA observations in epoch 2018.83. An overlap of about 100 km s⁻¹ is visible. The green and red arrows represent the velocities of the water maser components M1 and M2, respectively, as detected in the present work. The (tentative) blueshifted component reported in Pesce et al. (2015) is highlighted with the blue question mark.