# 6.7 GHz variability characteristics of new periodic methanol maser sources

## TL;DR

This study reports the discovery of five new periodic methanol maser sources with diverse variability patterns, providing insights into the physical conditions and structures around high-mass young stellar objects.

## Contribution

It introduces five newly identified periodic methanol masers and analyzes their variability patterns and physical implications, including disk structures and excitation mechanisms.

## Key findings

- Five new periodic maser sources discovered.
- Variability periods range from 149 to 540 days.
- Evidence of disk structures and complex excitation conditions.

## Abstract

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 $\sim$80 d occurred in G30.400$-$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.