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.
@article{arxiv.1904.02649,
title = {6.7 GHz variability characteristics of new periodic methanol maser sources},
author = {Mateusz Olech and Marian Szymczak and Paweł Wolak and Rafał Sarniak and Anna Bartkiewicz},
journal= {arXiv preprint arXiv:1904.02649},
year = {2020}
}