arXiv subjects

Gordon MacLeod

Publications and source records attributed to Gordon MacLeod.

3 recordsLinked to original sources

arXiv2025

The Extraordinary Maser Flaring Event in the Massive Protostellar System NGC6334I: Multi-Epoch Milliarcsecond Resolution Investigation of the 6.7-GHz Methanol Masers

We report the first multi-epoch milliarcsecond resolution imaging of the 6.7-GHz class II methanol maser emission associated with the high-mass protocluster system NGC6334I. The observations covered a period of over 10 years in four epochs between March 2010 and March 2020. We confirmed for the first time the emergence of 6.7-GHz methanol maser emission associated with NGC6334I-MM1, which lies north of the previously known sites of class IImethanol masers, NGC6334-MM2 and MM3. The new maser emission was located close to the strongest (sub)millimetre source in NGC6334I-MM1, identified as MM1-B, which experienced a sudden increase in intensity in 2015, produced by an episodic accretion event. We are able to compare the location and intensity of the 6.7-GHz methanol maser emission among the epochs before, during, and after the flare, providing new insights into the relationship between maser flares and episodic accretion events in high-mass stars.

astro-ph.GA↗

arXiv2019

Understanding Accretion Outbursts in Massive Protostars through Maser Imaging

The bright maser emission produced by several molecular species at centimeter to long millimeter wavelengths provides an essential tool for understanding the process of massive star formation. Unimpeded by the high dust optical depths that affect shorter wavelength observations, the high brightness temperature of these emission lines offers a way to resolve accretion and outflow motions down to scales below $\sim$1 au in deeply embedded Galactic star-forming regions at kiloparsec distances. The recent identification of extraordinary accretion outbursts in two high-mass protostars, both of which were heralded by maser flares, has rapidly impacted the traditional view of massive protostellar evolution, leading to new hydrodynamic simulations that can produce such episodic outbursts. In order to understand how these massive protostars evolve in response to such events, larger, more sensitive ground-based centimeter wavelength interferometers are needed that can simultaneously image multiple maser species in the molecular gas along with faint continuum from the central ionized gas. Fiducial observations of a large sample of massive protostars will be essential in order to pinpoint the progenitors of future accretion outbursts, and to quantify the outburst-induced changes in their protostellar photospheres and outflow and accretion structures. Knowledge gained from these studies will have broader impact on the general topic of accretion onto massive objects.

astro-ph.SR↗

arXiv2018

Multi-epoch VLBI of a double maser super burst

In a rare and spectacular display, two well-known massive star forming regions, W49N and G25.65+1.05, recently underwent maser 'super burst' - their fluxes suddenly increasing above 30,000 and 18,000 Jy, respectively, reaching several orders of magnitude above their usual values. In quick-response, ToO observations with the EVN, VLBA and KaVA were obtained constituting a 4 week campaign - producing a high-cadence multi-epoch VLBI investigation of the maser emission. The combination of high-resolution, polarisation and flux monitoring during the burst provides one of the best accounts, to date, of the maser super burst phenomenon, aiding their use as astrophysical tools. These proceedings contain the preliminary results of our campaign.

astro-ph.SR↗