We report on a long-term single-dish and VLBI monitoring for intermittent flare activities of a Dominant Blue-Shifted H _ { 2 } O Maser ( DBSM ) associated with a southern high mass young stellar object , G353.273+0.641 .
Bi-weekly single-dish monitoring using Hokkaido University Tomakomai 11-m radio telescope has shown that a systematic acceleration continues over four years beyond a lifetime of individual maser features .
This fact suggests that the H _ { 2 } O maser traces a region where molecular gas is steadily accelerated .
There were five maser flares during five-years monitoring , and maser distributions in four of them were densely monitored by the VLBI Exploration of Radio Astrometry ( VERA ) .
The overall distribution of the maser features suggests the presence of a bipolar jet , with the 3D kinematics indicating that it is almost face-on ( inclination angle of \sim 8 ^ { \fdg } –17 ^ { \fdg } from the line-of-sight ) .
Most of maser features were recurrently excited within a region of 100 \times 100 AU ^ { 2 } around the radio continuum peak , while their spatial distributions significantly varied between each flare .
This confirms that episodic propagations of outflow shocks recurrently invoke intermittent flare activities .
We also measured annual parallax , deriving the source distance of 1.70 ^ { +0.19 } _ { -0.16 } kpc that is consistent with the commonly-used photometric distance .