The evolution of the H₂O maser emission in the accretion burst source G358.93−0.03^⋆

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: olga.bayandina@inaf.it
² National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
³ Joint Institute for VLBI ERIC, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁴ Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
⁶ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁷ Dublin Institute for Advanced Studies, School of Cosmic Physics, Astronomy & Astrophysics Section, 31 Fitzwilliam Place, Dublin 2, Ireland
⁸ Space Research Unit, Physics Department, North-West University, Potchefstroom 2520, South Africa
⁹ Department of Physics and Astronomy, University of Nigeria, Carver Building, 1 University Road, Nsukka 410001, Nigeria
¹⁰ SARAO, Hartebeesthoek Radio Astronomy Observatory, PO Box 443, Krugersdorp 1741, South Africa
¹¹ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Antig. Carr. a Patzcuaro 8701, Morelia 58089, Mexico
¹² Ural Federal University, 51 Lenin Str., 620051 Ekaterinburg, Russia
¹³ National Astronomical Research Institute of Thailand (Public Organization), 260 Moo 4, T. Donkaew, A. Maerim, Chiang Mai 50180, Thailand
¹⁴ Astro Space Center, P.N. Lebedev Physical Institute of RAS, 84/32 Profsoyuznaya st., Moscow 117997, Russia
¹⁵ Center for Astronomy, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan

Received: 23 May 2022
Accepted: 15 June 2022

Abstract

Context. 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.

Aims. 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).

Methods. 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.

Results. 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.

Conclusions. 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.