Radio Observations of Active Galactic Nuclei
Session 102 -- Invited Talks
Invited presentation, Friday, January 14, 4:00-5:30, Salons III/IV Room (Crystal Gateway)

## [102.02] Radio Observations of Active Galactic Nuclei

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Very Long Baseline Interferometry (VLBI) has come of age with the completion of the Very Long Baseline Array (VLBA). In addition to this remarkable new facility, important advances in observing techniques and data analysis over the last few years have ushered in a new era of study of the nuclei of active galaxies. These include snapshots and polarization and phase referencing observations --- all new techniques which are primed to take advantage of the VLBA. Snapshots make possible the VLBI imaging of large samples of objects and in the last year have led to the discovery of a previously unsuspected class of active galaxies - the Compact Symmetric Objects (COS's), which have an active phase which lasts typically $3\,\times\,10^3$ years, and whose energy requirements could be accommodated by the capture of a single star by a quiescent supermassive black hole at the center of an elliptical galaxy. VLBI snapshots of large samples of objects are also now providing interesting limits on a wide range of gravitational lens masses. VLBI polarization observations have shown a very distinctive difference between the magnetic field configuration in quasars and BL Lac objects. \vskip 6pt \noindent The first results from the VLBA demonstrate its power and potential as an imaging device. These will be discussed in the context of the above developments, and with emphasis on remarkable new images of the nuclear emission region in NGC 1275 (3C84).