Linear Polarization of Class I Methanol Masers in Massive Star-Forming
  Regions
  Class I methanol masers are found to be good tracers of the interaction
between outflows from massive young stellar objects with their surrounding
media. Although polarization observations of Class II methanol masers have been
able to provide information about magnetic fields close to the central
(proto)stars, polarization observations of Class I methanol masers are rare,
especially at 44 and 95 GHz. We present the results of linear polarization
observations of 39 Class I methanol maser sources at 44 and 95 GHz. These two
lines are observed simultaneously with one of the 21 m Korean VLBI Network
telescopes in single-dish mode. Approximately 60% of the observed sources have
fractional polarizations of a few percent in at least one transition. This is
the first reported detection of linear polarization of the 44 GHz methanol
maser. The two maser transitions show similar polarization properties,
indicating that they trace similar magnetic environments, although the fraction
of the linear polarization is slightly higher at 95 GHz. We discuss the
association between the directions of polarization angles and outflows. We also
discuss some targets having different polarization properties at both lines,
including DR21(OH) and G82.58+0.20, which show the 90{\deg} polarization angle
flip at 44 GHz.
