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 per cent 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.

Discovery of periodic maser emission was an unexpected result from monitoring observations of methanol transitions in high-mass young stellar objects. We report on the detection of five new periodic sources from a monitoring program with the Torun 32 m telescope. Variability with a period of 149 to 540 d and different patterns from sinusoidal-like to intermittent was displayed. Three dimensional structure of G59.633−0.192 determined from the time delays of burst peaks of the spectral features and high angular resolution map implies that the emission traces a disk. For this source the 6.7 GHz light curve followed the infrared variability supporting a radiative scheme of pumping. An unusual time delay of ∼80 d occurred in G30.400−0.296 could not be explained by the light travel time and may suggest a strong differentiation of physical conditions and excitation in this deeply embedded source. Our observations suggest the intermittent variability may present a simple response of maser medium to the underlying variability induced by the accretion luminosity while other variability patterns may reflect more complex changes in the physical conditions.

We suggest a hybrid plasmonic device made of a bimodal metallic nanoantenna coupled to an incoherently pumped quantum emitter. This device emits light into the two modes entangled in the number of photons. The process is a prime example for losses turning from a nuisance into something beneficial, since, even though counterintuitively, the entanglement is enabled by strong incoherent processes, i.e. dominant scattering and absorption rates of the nanoantenna. This renders the nanoantenna an active source of nonclassicality. Both, the high emission rate and the degree of entanglement of the emitted light are insensitive with respect to imperfections in the nanoantenna length, rendering the scheme feasible for an implementation.

Methanol masers observed at high angular resolution are useful tool to investigate the processes of high-mass star formation. Here, we present the results of statistical analysis of the 6.7 GHz methanol maser structures in 60 sources observed with the EVN. The parameters of the maser clouds and exciting stars were derived. There is evidence that the emission structures composed of larger number of maser clouds are formed in the vicinity of more luminous exciting stars.