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\section{Other mega-maser detections}  \label{sec:other}  While the vast majority of detections and observational effort has focussed on detecting OH and H$_2$O mega-masers, upgrades to some radio telescopes have lead to the first detections of CH$_3$OH and SiO mega-masers \citep{wang2014_SiO_CH3OH, chen_methanol_2015}. Both of these species have widespread galactic emission: SiO masers are associated with circumstellar material around late-type stars, and CH$_3$OH masers are commonly observed in star-forming regions of dense molecular gas \citep{Elitzur_1992}. Properties of the SiO line are shown in Table \ref{tab:???} \ref{tab:maser_props}  The first, and only, H$_2$CO mega-maser was reported by \citet{baan1986} towards IC 4553 (in the well-studied Arp 220 system). IC 4553 was the first detection of on OH mega-maser. \citet{baan1986} find similar velocity components in between the two mega-maser detections. It's possible that H$_2$CO mega-masers coincide with other OH mega-masers, however they may be too faint to observe with current instrumentation. The flux density of the H$_2$CO maser is nearly 100 times fainter than the OH detection. Too little is known about this class of mega-masers to infer an accurate relation to OH mega-masers.  The first detections of SiO and CH$_{3}$OH mega-masers are reported by \citet{wang2014_SiO_CH3OH} in observations towards NGC 1068 using the IRAM 30m telescope. This source has a previously discovered H$_2$O mega-maser \citep{Gallimore_2001}. The velocities components of the SiO nearly match those of the H$_2$O emission, indicating that the SiO likely also arises due to the compact, nuclear disk (see \S\ref{sub:h2o_props}). (\S\ref{sub:h20_agn}).  The CH$_3$OH exhibit different velocities and linewidths than the SiO emission. The author's propose that this emission arises from a shock front associated with a nuclear jet or a molecular outflow. Future high-resolution observations with ALMA may allow for AGN feedback to be studied from the nuclear disk out to $\sim 100$ pc using maser emission of these three species. If SiO mega-masers do, in fact, trace the nuclear disk as the H$_2$O ones do, they may be used for the same applications discussed in \S\ref{sec:h2o_mm}. A second detection of CH$_3$OH mega-masers was recently reported by \citet{chen_methanol_2015} toward the well-studied Arp 220, which is also known to harbour OH and H$_2$CO mega-maser emission. They report a detection of CH$_3$OH in the same 36.2 GHz line as \citet{wang2014_SiO_CH3OH} and at 37.7 GHz using the Australia Telescope Compact Array. The observed spectral features are narrow and their inferred luminosities are about 8 orders of magnitude greater than typical galactic CH$_3$OH masers, putting them nearly in the {\it giga}-maser regime. They also conclude that this emission arises due to shock fronts associated with outflows from the nuclear region. They find the position of the mega-masers correlate well with H$\alpha$ emission. These results suggest that CH$_3$OH mega-masers may trace larger scales than OH and H$_2$O mega-masers. Through combined detections of these three species in a system, the influence of the circumnuclear starburst on the surrounding regions could be tested.