44 GHz methanol masers: Observations toward 95 GHz methanol masers
  We report a simultaneous 44 and 95 GHz class I methanol maser survey toward
144 sources from the 95 GHz class I methanol maser catalog. The observations
were made with the three telescopes of the Korean very long baseline
interferometry network operating in single-dish mode. The detection rates are
89% at 44 GHz and 77% at 95 GHz. There are 106 new discoveries at 44 GHz.
Comparing the previous 95 GHz detections with new observations of the same
transitions made using the Purple Mountain Observatory 13.7 m radio telescope
shows no clear evidence of variability on a timescale of six years. Emission
from the 44 and 95 GHz transitions shows strong correlations in peak velocity,
peak flux density, and integrated flux density, indicating that they are likely
cospatial. We found that the peak flux density ratio Spk,95/Spk,44 decreases as
the 44 GHz peak flux density increases. We found that some class I methanol
masers in our sample could be associated with infrared dark clouds, while
others are associated with H II regions, indicating that some sources occur at
an early stage of high-mass star formation, while others are located toward
more evolved sources.
