Periodic variability of the mainline hydroxyl masers in G9.62+0.20E

We present the results of a monitoring campaign using the KAT-7 and HartRAO 26 m telescopes, of hydroxyl, methanol, and water vapour masers associated with the high-mass star-forming region G9.62+0.20E. Periodic flaring of the mainline hydroxyl masers was found, similar to that seen in the 6.7 and 12.2 GHz methanol masers. The 1667 MHz flares are characterized by a rapid decrease in flux density, which is coincident with the start of the 12.2 GHz methanol maser flare. The decrease in the OH maser flux density is followed by a slow increase till a maximum is reached after which the maser decays to its pre-flare level. A possible interpretation of the rapid decrease in the maser flux density is presented. Considering the projected separation between the periodic methanol and OH masers, we conclude that the periodic 12.2 methanol masing region is located about 1600 au deeper into the molecular envelope compared to the location of the periodic OH masers. A single water maser flare was also detected, which seems not to be associated with the same event that gives rise to the periodic methanol and OH maser flares.