Daily Monitoring of the Variability of the Cepheus A Methanol Maser at 6.7 GHz

We detected a rapid variability of 6.7-GHz methanol maser for Cepheus A (Cep A) using Yamaguchi 32-m radio telescope. Two of five spectral features decrease in flux density down to 50% for 27 days, while flux density of other three features increase up to 300%. The time variation of this maser flux density showed a clear inverse correlation between the decayed and the rising features. The synchronous of the variation would suggest that the Cep A methanol maser was excited by infrared radiation from a common exciting source. Given an isolation in a point of view of radial velocities and a spatial distribution in each feature, the inverse correlation would be caused by a variation of the suitable dust temperature in the regions producing methanol maser emission with accompanying a variation of flux density of the exciting source radiation.