First detections of methanol maser lines from a rare transition family
We report the first observations in a rare family of class II methanol maser transitions in both CH$_3$OH and $^{13}$CH$_3$OH toward three southern high-mass star formation regions, along with the first maser detected in the $^{13}$CH$_3$OH line. The $8_2 \rightarrow 9_1 A^{-}$ methanol transition was observed in both CH$_3$OH and $^{13}$CH$_3$OH (at 28.9 GHz and 41.9 GHz respectively) toward three sources; G358.93-0.03, NGC6334I and G345.01+1.79, all of which are star formation regions with recent maser flaring events. We report the first maser detection of the 41.9 GHz line in $^{13}$CH$_3$OH toward G358.93-0.03 and the first confirmed maser detection of the 28.9 GHz line in CH$_3$OH toward NGC6334I. Additionally we report a maser detection of the 28.9 GHz line in CH$_3$OH toward G358.93-0.03, meaning that with our detection of the 41.9 GHz line, this is the first isotopic detection of these lines toward G358.93-0.03. The newly detected maser transitions are associated with the primary millimetre continuum sources (MM1) in both G358.93-0.03 and NGC6334I, within the varying positional uncertainties.