Ten Milliparsec-Scale Structure of the Nucleus Region in Centaurus A

We present the results of a VLBI Space Observatory Programme (VSOP)observation of the subparsec structure in Centaurus A at 4.9 GHz. Owing to itsproximity, our Centaurus A space-VLBI image is one of the highest spatialresolution images of an AGN ever made -- 0.01 pc per beam. The elongated coreregion is resolved into several components over 10 milli-arcseconds long (0.2pc) including a compact component of brightness temperature 2.2x10^10K. Weanalyze the jet geometry in terms of collimation. Assuming the strongestcomponent to be the core, the jet opening angle at ~ 5,000 r_s (Schwarzchildradii) from the core is estimated to be ~ 12 degree, with collimation of thejet to ~ 3 degree continuing out to ~ 20,000 r_s. This result is consistentwith previous studies of the jet in M87, which favor MHD disk outflow models.Future space VLBI observations at higher frequencies will probably be able toimage the collimation region, within 1,000 r_s of the center of Centaurus A,together with the accretion disk itself.Comment: 12 pages, 6 figures, accepted for publication in PASJ, Vol.57 No.6, VSOP special issu