The Dense Plasma Torus around the Nucleus of an Active Galaxy NGC1052

A subparsec-scale dense plasma torus around an active galactic nucleus (AGN)is unveiled. We report on very-long-baseline interferometry (VLBI) observationsat 2.3, 8.4, and 15.4 GHz towards the active galaxy NGC 1052. The convexspectra of the double-sided jets and the nucleus imply that synchrotronemission is obscured through free--free absorption (FFA) by the foreground colddense plasma. A trichromatic image was produced to illustrate the distributionof the FFA opacity. We found a central condensation of the plasma which coversabout 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. Asimple explanation for the asymmetric distribution is the existence of a thickplasma torus perpendicular to the jets. We also found an ambient FFA absorber,whose density profile can be ascribed to a spherical distribution of theisothermal King model. The coexistence of torus-like and sphericaldistributions of the plasma suggests a transition from radial accretion torotational accretion around the nucleus.Comment: 10 pages, to appear in Publ. Astron. Soc. Japan, vol.53, No.2 (2001