Physics of compact nonthermal sources. III - Energetic considerations

Abstract

Equations are given for calculating the energy content of compact incoherent electron-synchrotron sources Numerical results are given in tables for 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, assuming that the low-frequency turnovers in the radio spectra are due to self-absorption and that the electron distribution is isotropic. Variants on the canonical model involving (a) alternative explanations for the low-frequency turnover, (b) relativistic motions of different types, (c) proton- rather than electron-synchrotron radiation, are discussed. The derived parameters are very sensitive to the adopted source decomposition and to the angular size. Conversely, the very weak dependence of the observables upon details of the physical properties adds insight to the Compton luminosity explanation given by Kellermann and Pauliny-Toth for the nearly constant maximum brightness temperature. Lower limits to the calculated total energies in electrons and magnetic field range from about 1052 to 1058 ergs if no corrections are made for possible relativistic motion in some sources. If the rapid time variations in 3C 454.3 and CTA 102 are produced by highly relativistic motion (y0 ^ 20), then the resulting increase in the magnetic energy, and the energy expended in the expansion of the source in a gaseous medium, may lead to total energy requirements well in excess of 1060 ergs. Since outbursts have been observed every few years, the total energy expended could be very large indeed. Conventional ways of accounting for this energy may then be inadequate unless the sources are closer than their cosmological distances. The importance of VLBI and scintillation monitoring of some sources to decide between the canonical inter- pretations and some classes of alternatives is stressed.