2021MNRAS.500.3425M

The source G9.62+0.20E surprises again! Several of the associated 6.7- and 12.2-GHz methanol masers are experiencing contemporaneous and systematic velocity drifts. Both 6.7- and 12.2-GHz methanol features blueward of v = +1.2 km s^–1 are blue shifting while those redward are red shifting. A best-fitting rotating Keplerian disc with a central mass of ∼12 M_☉, radii R_inner = 5 au and R_outer = 5000 au, and at an inclination angle of 22^* either precessing and/or experiencing infall explains these systematic velocity drifts. Also three more distinct 6.7-GHz methanol maser features are found to vary periodically; two very weak and one obviously periodic only after 2003. Evidence of periodicity is seen as early as 1992. Time lags are confirmed but the cause is unclear. It is possible this source will surprise again.