The evolution of the H2O maser emission in the accretion burst source G358.93-0.03

TL;DR

This study investigates the evolution of 22 GHz water maser emission in the massive young stellar object G358.93-0.03 during an accretion burst, revealing significant changes in maser distribution and morphology linked to the burst event.

Contribution

It provides the first detailed VLA observations of water maser evolution before and after an accretion burst in G358.93-0.03, highlighting the impact of the burst on maser distribution and ejection processes.

Findings

Maser distribution drastically changed post-burst

Maser morphology and velocity extent were altered

Accretion burst influenced surrounding maser regions

Abstract

The massive young stellar object (MYSO) G358.93-0.03-MM1 showed an extraordinary near-infrared- to (sub-)millimetre-dark and far-infrared-loud accretion burst, which is closely associated with flares of several class II methanol maser transitions, and, later, a 22 GHz water maser flare. Water maser flares provide an invaluable insight into ejection events associated with accretion bursts. Although the short timescale of the 22 GHz water maser flare made it impossible to carry out a very long baseline interferometry observation, we could track it with the Karl G. Jansky Very Large Array (VLA). The evolution of the spatial structure of the 22 GHz water masers and their association with the continuum sources in the region is studied with the VLA during two epochs, pre- and post-H2O maser flare. A drastic change in the distribution of the water masers is revealed: in contrast to the four maser groups detected during epoch I, only two newly formed clusters are detected during epoch II. The 22 GHz water masers associated with the bursting source MM1 changed in morphology and emission velocity extent. Clear evidence of the influence of the accretion burst on the ejection from G358.93-0.03-MM1 is presented. The accretion event has also potentially affected a region with a radius of ~2'' (~13 500 AU at 6.75 kpc), suppressing water masers associated with other point sources in this region.