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L. J. Greenhill (CfA), J. R. Herrnstein (NRAO), S. P. Ellingsen (UTas), J. E. Reynolds, R. P. Norris (ATNF), J. M. Moran (CfA), R. S. Booth (OSO)
The Circinus galaxy is a luminous Seyfert 2 object within which the central engine is heavily obscured, so much so that even hard X-ray emission (2-10 keV) is blocked. However, the large column of dust and gas does not attenuate centimeter wavelength radiation, and it is notable that this AGN is a source of strong water maser emission. We have used the Long Baseline Array of the Australia Telescope, to map the distribution of maser emission at two epochs separated by 1 month. The data resolve the emission with resolutions of about 1 km/s and 0.02 pc. The masers trace a thin accretion disk about 0.8 pc in radius that is bound by a massive central object, in accord with expectations shaped by the current AGN paradigm. However, there is also a significant population of masers that lie away from the disk, possibly in an outflow. A comparison of the images from the two epochs suggests that these masers vary significantly on time scales of 1 month, more rapidly than the masers in the disk. The preponderance of outflow-borne masers sets Circinus apart from the other established cases of water masers in accretion disks, i.e., NGC4258, NGC1068, and NGC4945.