SYNCHROTRON EMISSION FROM SHOCKED RELATIVISTIC JETS .3. MODELS FOR THE CENTIMETER WAVE BAND QUIESCENT AND BURST EMISSION FROM 3C-279 AND OT-081

We present models for the radio emission from the sources 3C 279 and OT 081 (1749 + 096) based on a diverging flow of synchroton plasma with both axial and tangled magnetic field components. Outbursts are due to shocks that locally compress the field, allowing for a significant degree of polarized emission from the shocked parts of the flow. We demonstrate that short time scale activity evident in the polarized flux is compatible with the contemporaneous, long time scale, apparently single outbursts in the total flux. This effect arises in part because high opacity restricts the duration of the polarized outbursts, keeping them distinct and in part because of the cancellation between orthogonal polarizations associated with the axial and the compressed, tangled magnetic fields. We estimate that the axial magnetic field contains approximately 5%-15% of the magnetic energy density. Model maps of 3C 279 are in qualitative agreement with VLBI maps and suggest that components on VLBI maps that are widely spaced in time, which hiterto have been assumed to be a single, evolving component, are in fact a number of discrete events. The comparison demonstrates the need for both high time-resolution mapping and a more detailed description of the flow hydrodynamics if source evolution is to be interpreted unambiguously. There is evidence for changes in the properties of the preexisting flow at some epochs-distinct from those associated with shocks, and presumably related to changes in the flow at or near the "central engine." We compare the models of 3C 279 and OT 081 with that of BL Lacertae and conclude that the major difference between these sources is that BL Lacertae exhibits much less opacity and a weaker axial field.