VLBI observations of the radio sources 0552 + 398 and 1848 + 283 - Measurements of the departure from equipartition

Abstract

Very Long Baseline Interferometer observations at 5 and 10.6 GHz, together with multifrequency flux density measurements, are reported for the compact radio sources 0552 + 398 and 1848 + 283. Both sources are characterized by sharply peaked spectra with maxima in the 5-10 GHz range and are thus good approximations to the theoretical ideal of a homogeneous synchrotron source. The data are used to determine the magnetic field strengths in these sources, which have been compared with the 'equipartition magnetic field' estimates. In the source 0552 + 398, the field is weaker (by a factor of about 100) than the equipartition value. On the other hand, the observations of 1848 + 283 are consistent with this source possessing roughly equal energy densities in the magnetic field and relativistic electrons.