2023AJ....166...21Z

We report the detection of the disk/torus, outflow, and inflow structures traced by H₂O masers toward a high-mass young stellar object W51 North during its H₂O maser outburst stage using the Karl G. Jansky Very Large Array (VLA). It is found that the disk has a radius of ∼4000 au and an inclination angle with respect to the sky plane of ∼60° by combining the VLA and the Atacama Large Millimeter/submillimeter Array data. Additionally, a peculiar flow perpendicular to the SiO bipolar outflow is detected in the H₂O maser, SiO, and HC₃N lines, which is newly-identified as an infalling streamer rather than an old outflow from this source, as reported in previous studies. Combining the VLA map and the Tianma radio telescope monitoring of the H₂O masers suggests that the origin of the luminosity outburst of H₂O masers during 2020 January-April is likely related to the energy release from the collision between the infalling streamer and the disk. This may provide an additional mechanism to account for the luminosity outburst or episodic accretion beyond disk fragmentation caused by gravitational instability.