Detection of 84-GHz class I methanol maser emission towards NGC 253
  We have investigated the central region of NGC 253 for the presence of
84.5-GHz ($5_{-1}\rightarrow4_0$E) methanol emission using the Australia
Telescope Compact Array. We present the second detection of 84.5-GHz class~I
methanol maser emission outside the Milky Way. This maser emission is offset
from dynamical centre of NGC 253, in a region with previously detected emission
from class~I maser transitions (36.2-GHz $4_{-1}\rightarrow3_0$E and 44.1-GHz
$7_{0}\rightarrow6_1$A$^{+}$ methanol lines) . The emission features a narrow
linewidth ($\sim$12 km s$^{-1}$) with a luminosity approximately 5 orders of
magnitude higher than typical Galactic sources. We determine an integrated line
intensity ratio of $1.2\pm0.4$ between the 36.2 GHz and 84.5-GHz class I
methanol maser emission, which is similar to the ratio observed towards
Galactic sources. The three methanol maser transitions observed toward NGC 253
each show a different distribution, suggesting differing physical conditions
between the maser sites and that observations of additional class~I methanol
transitions will facilitate investigations of the maser pumping regime.
