The Extraordinary Outburst in the Massive Protostellar System NGC6334I-MM1: Spatio-kinematics of Water Masers during a Contemporaneous Flare Event

TL;DR

This study observes water maser proper motions in the massive star-forming region NGC6334I-MM1 following an accretion burst, revealing high-velocity motions aligned with jet axes and complex outflow interactions.

Contribution

It provides detailed measurements of water maser proper motions during a flare event, linking maser kinematics to jet activity and outflow structures in a massive protostellar system.

Findings

High velocity water maser motions (~85 km/s) detected in multiple clusters.

Maser motions align with jet and outflow axes, indicating shock interactions.

Proper motions suggest jet-driven shocks post-accretion burst.

Abstract

Following an eruptive accretion event in NGC6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly variable water masers associated with the massive star-forming region, NGC6334I. High velocity H$_2$O maser proper motions were detected in 5 maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1 and UCHII-W3. The overall average of the derived relative proper motion is 85 km s$^{-1}$. This mean proper motion is in agreement with the previous results from VLA multi-epoch observations. Our position and velocity variance and co-variance matrix analyses of the maser proper motions show its major axis to have a position angle of $-$79.4$^\circ$, cutting through the dust cavity around MM1B and aligned in the northwest-southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast-southwest bipolar outflow, CS(6-5) north-south collimated bipolar outflow, and the radio jet. The relative proper motions of the H$_2$O masers in UCHII-W1 are likely not driven by the jets of MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H$_2$O masers trace shocks of jet motion.