Physics of Compact Nonthermal Sources. H. Determination of Physical Parameters

Abstract

In Paper I a set of restrictions upon the magnetic field and visible angular size of a canonical nonthermal source (one whose emission is incoherent electron synchrotron) were obtained. The degree of electron anisotropy and magnetic field disordering were left as free parameters. In the present paper these restrictions are applied to the variable compact radio sources 3C 84, 3C 120, 3C 273, 3C 279, 3C 454.3, CTA 102, 3C 446, PKS 2134+ 004, VRO 42.22.01, and OJ 287. The theoretically derived angular sizes for these sources are in reasonable agreement with published VLBI sizes provided that the characteristic pitch angles are not extremely small. The magnetic field strengths determined from the degree of circular polarization are generally compatible with field strengths derived from the self-absorption and synchrotron self-Compton conditions, again provided that the pitch angles are not too small. It is argued that the self-absorption optical depth cannot be much less than unity near the low-frequency turnovers; otherwise, serious discrepancies with observation result. The derived magnetic fields are generally less than the equipartition fields, indicating the sources are matter dominated. When placed at their redshift distances, most of the sources appear to vary with a time scale comparable to the light travel time across the source. However, for 3C 454.3 and CTA 102, time scales much shorter than the light travel time are observed. It is shown that multiple bursts of small canonical sources will not adequately explain this phenomenon unless extreme relativistic effects are included. Alternative explanations are briefly discussed. Conservative upper limits to the distance of VRO 42.22.01 (BL Lac) and OJ 287 based on light travel time arguments are 80 and 500 Mpc, respectively, unless highly relativistic motions are invoked. Subject headings: quasi-stellar sources or objects - radio sources - synchrotron radiation