  We report the discovery of the Zeeman effect in the 44 GHz Class I methanol
maser line. The observations were carried out with 22 antennas of the EVLA
toward a star forming region in OMC-2. Based on our adopted Zeeman splitting
factor of z = 1.0 Hz/mG, we detect a line of sight magnetic field of 18.4 +/-
1.1 mG toward this source. Since such 44 GHz methanol masers arise from shocks
in the outflows of star forming regions, we can relate our measurement of the
post-shock magnetic field to field strengths indicated by species tracing
pre-shock regions, and thus characterize the large scale magnetic field.
Moreover, since Class I masers trace regions more remote from the star forming
core than Class II masers, and possibly earlier phases, magnetic fields
detected in 6.7 GHz Class II and 36 GHz and 44 GHz Class I methanol maser lines
together offer the potential of providing a more complete picture of the
magnetic field. This motivates further observations at high angular resolution
to find the positional relationships between Class I and Class II masers, and
masers at various frequencies within each category. In particular, methanol
masers are widespread in high- as well as intermediate-mass star forming
regions, and our discovery provides a new method of studying the magnetic field
in such regions, by observing small physical scales that are not accessible by
any other lines.
