The Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward
  DR21(OH)
  We report the detection of the Zeeman effect in the 44 GHz Class I methanol
maser line toward the star forming region DR21(OH). In a 219 Jy/beam maser
centered at an LSR velocity of 0.83 km s$^{-1}$, we find a 20-$\sigma$
detection of $zB_{\text{los}} = 53.5 \pm 2.7$ Hz. If 44 GHz methanol masers are
excited at $n \sim 10^{7-8}$ cm$^{-3}$, then the $B~vs.~n^{1/2}$ relation would
imply from comparison with Zeeman effect detections in the CN($1-0$) line
toward DR21(OH) that magnetic fields traced by 44 GHz methanol masers in
DR21(OH) should be $\sim$10 mG. Together with our detected $zB_{\text{los}} =
53.5$ Hz, this would imply that the value of the 44 GHz methanol Zeeman
splitting factor $z$ is $\sim$5 Hz mG$^{-1}$. Such small values of $z$ would
not be a surprise, as the methanol molecule is non paramagnetic, like H$_2$O.
Empirical attempts to determine $z$, as demonstrated, are important because
currently there are no laboratory measurements or theoretically calculated
values of $z$ for the 44 GHz methanol transition. Data from observations of a
larger number of sources are needed to make such empirical determinations
robust.
