2011MNRAS.417..238M

We have performed very long baseline interferometry (VLBI) and single-dish monitoring of 22-GHz H₂ O maser emission from the high-mass young stellar object G353.273+0.641 with the VLBI Exploration of Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Two maser flares have been detected, separated by almost two years. Frequent VLBI monitoring has revealed that the flare activity has been accompanied by structural change of the prominent shock front traced by H₂ O maser alignments. We have detected only blueshifted emission and all maser features have been distributed within a very small area of 200 {x} 200 au², in spite of a wide velocity range (>100 km/s). The light curve shows notably intermittent variation and suggests that the H₂ O masers in G353.273+0.641 are excited by an episodic radio jet. The time-scale of ∼2 yr and characteristic velocity of ∼500 km/s also support this interpretation. Two isolated velocity components, C50 (-53 ± 7 km/s) and C70 (-73±7 km/s), have shown synchronized linear acceleration of the flux-weighted {img} values (∼ -5 km/s/yr) during the flare phase. This can be converted to the lower-limit momentum rate of 1.1 {x} 10^–3 M_☉ km/s/yr. The maser properties are quite similar to those of IRAS 20126+4104 especially. This corroborates the previous suggestion that G353.273+0.641 is a candidate high-mass protostellar object. The possible pole-on geometry of the disc–jet system may be suitable for direct imaging of the accretion disc in this case.