Monitoring observations of 6.7 GHz methanol masers
arXiv:1710.04595 · doi:10.1093/mnras/stx2693
Abstract
We report results of 6.7 GHz methanol maser monitoring of 139 star-forming sites with the Torun 32 m radio telescope from June 2009 to February 2013. The targets were observed at least once a month, with higher cadences of 2-4 measurements per week for circumpolar objects. Nearly 80 percent of the sources display variability greater than 10 per cent on a time-scale between a week and a few years but about three quarters of the sample have only 1-3 spectral features which vary significantly. Irregular intensity fluctuation is the dominant type of variability and only nine objects show evidence for cyclic variations with periods of 120 to 416 d. Synchronised and anti-correlated variations of maser features are detected in four sources with a disc-like morphology. Rapid and high amplitude bursts of individual features are seen on 3-5 occasions in five sources. Long (>50 d to 20 months) lasting bursts are observed mostly for individual or groups of features in 19 sources and only one source experienced a remarkable global flare. A few flaring features display a strong anti-correlation between intensity and line-width that is expected for unsaturated amplification. There is a weak anti-correlation between the maser feature luminosity and variability measure, i.e. maser features with low luminosity tend to be more variable than those with high luminosity. The analysis of the spectral energy distribution and continuum radio emission reveals that the variability of the maser features increases when the bolometric luminosity and Lyman flux of the exciting object decreases. Our results support the concept of a major role for infrared pumping photons in triggering outburst activity of maser emission.
References in corpus (11)
- Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
- A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
- On the Relationship of UC H II Regions and Class II Methanol Masers: I. Source Catalogs
- On the Class II Methanol Maser Periodic Variability due to the Rotating Spiral Shocks in the Gaps of Disks Around Young Binary Stars
- The almost ubiquitous association of 6.7 GHz methanol masers with dust
- Methanol Maser Associated Outflows: Detection statistics and properties
- A multi-transition molecular line study of candidate massive young stellar objects associated with methanol masers
- Discovery of four periodic methanol masers and updated light curve for a further one
- New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391
- Periodic Flare of the 6.7 GHz Methanol Maser in IRAS22198+6336
- Observations of the Bursting Activity of the 6.7GHz Methanol Maser in G33.641-0.228