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Session 51 - Active Galactic Nuclei & Quasars.
Oral session, Thursday, June 12
North Main Hall A,

[51.06] VLBA Imagess of 3C 454.3 at 43 GHz: The Nature of the Core

A. P. Marscher, E. M. Moore (Boston Univ.), S. G. Marchenko (Astron. Inst., St. Petersburg Univ.), J. L. Gómez (IAA), J. M. Mart\'\i, J. M. Ibáñez (U.Valencia), S. D. Bloom (NASA/GSFC), A. E. Wehrle, W. Xu (IPAC)

The evolution of the submilliarcsecond-scale structure of the quasar 3C 454.3 is revealed through a series of 10 images obtained over a two-year period (Jan 1995 -- Dec 1996). At all epochs, there is a jet along position angle about -80^\circ that appears to terminate at a feature that is extended in a direction perpendicular to the jet. The simplest interpretation is that this feature is stationary. In 1995, a component moved at an apparently superluminal velocity of 13c (for H_0 = 65 km s^-1 Mpc^-1 and q_0 \approx 0) down the jet, approaching the extended feature. The moving component first brightened, as the total flux density of the source rose at 43 GHz, then faded after April 1995.

There is no stationary feature at the narrow end of the jet, where the ``core'' is located in most superluminal radio sources. However, the appearance of a roughly stationary knot upstream from the site of emergence of the superluminal component is consistent with a model in which the core is a standing oblique shock whose location shifts somewhat as the Mach number of the jet is changed. This agrees with the behavior found in relativistic hydrodynamical simulations of jets. The position angle of the jet has changed since the 1980's, which suggests that the extended feature might be the site of partial energy deposition of a jet that interacts with ``fresh'' interstellar material as it changes direction.

This research is supported in part by NASA through the Gamma Ray Observatory Guest Investigator Program and the Astrophysical Theory Program.

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