2012ApJ...759L...5E

We have used the Swedish ESO Submillimetre Telescope (SEST) to search for new class II methanol maser transitions toward the southern source G 345.01+1.79. Over a period of 5 days, we observed 11 known or predicted class II methanol maser transitions. Emission with the narrow line width and characteristic velocity of class II methanol masers (in this source) was detected in eight of these transitions, two of which have not previously been reported as masers. The new class II methanol maser transitions are the 13_–3-12_–4 E transition at 104.1 GHz and the 5₁-4₂ E transition at 216.9 GHz. Both of these are from transition series for which there are no previous known class II methanol maser transitions. This takes the total number of known class II methanol maser series to 10, and the total number of transitions (or transition groups) to 18. The observed 104.1 GHz maser suggests the presence of two or more regions of masing gas with similar line of sight velocities, but quite different physical conditions. Although these newly discovered transitions are likely to be relatively rare, where they are observed, combined studies using the Australia Telescope Compact Array and the Atacama Large Millimeter Array offer the prospect to be able to undertake multi-transition methanol maser studies with unprecedented detail.