Short-period variability in the Class II methanol maser source G12.89+0.49 (IRAS 18089-1732)

Abstract

Time series are presented for the Class II methanol maser source G12.89+0.49, which has been monitored for nine years at the Hartebeesthoek Radio Astronomy Observatory. The 12.2 and 6.7 GHz methanol masers were seen to exhibit rapid, correlated variations on time-scales of less than a month. Daily monitoring has revealed that the variations have a periodic component with a period of 29.5 d. The period seems to be stable over the 110 cycles spanned by the time series. There are variations from cycle to cycle, with the peak of the flare occurring anywhere within an 11 d window, but the minima occur at the same phase of the cycle. Time delays of up to 5.7 d are seen between spectral features at 6.7 GHz and a delay of 1.1 d is seen between the dominant 12.2 GHz spectral feature and its 6.7 GHz counterpart