6.7GHz methanol maser variability in Cepheus A
  6.7 GHz methanol maser emission from the well-studied star-forming region
Cepheus A was monitored with the Torun 32 m radio telescope. We found
synchronized and anticorrelated changes of the flux density of the two
blueshifted and one redshifted maser features for ~30 per cent of 1340 d of our
observations. Two of those features exhibited high amplitude flux density
variations with periods of 84-87 d over the last 290 d interval of the
monitoring. We also report on two flares of emission at two different
redshifted velocities completely covered during the whole outburst. These flare
events lasted 510-670 d and showed a very rapid linear rise and slow
exponential decline, which may be caused by variability of the seed flux
density. The flux density of the two strongest features dropped by a factor of
2-5 on a time-scale ~22 yr, while other features have not changed significantly
during this period, but showed strong variability on time-scales <5 yr.
