1996A&A...312..738M

The structure of the quasar 3C 345 has been studied at λ49cm with a global VLBI network. The core has a low-frequency cut off in its spectrum, and is very weak at this wavelength. The most compact bright knot is the part of the jet nearest to the nucleus, with a size of ∼5x4mas and a brightness temperature of T_b∼0.6x10¹²K. Its flux density and solid angle increased by a factor of ∼2 during the period 1983.9 to 1990.8, but the brightness temperature did not change significantly. The emission at millimeter wavelengths decreased by a factor of ∼2 during the same period, while the UV emission from the nucleus also decreased. We suggest that variations in the low-frequency emission are caused by changes in the absorption by a cocoon - the thermal plasma surrounding the jet. The electron density in the core region is N_e∼10⁵cm^–3 and the longitudinal component of the magnetic field is ∼40µG. The emission measure and the rotation measure vary with r, the distance from the nucleus, as r^–3. The data at λ49cm indicate several components in and near the "hotspot" at the end of the arcsec jet.