The structure of the quasar 3C345 at lambda 49cm and its relation to low-frequency variability

• The structure of the quasar 3C345 has been studied at lambda 49cm with a global VLBI network. The core has a low-freuqncy 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 about 5x4 mas and a brightness temperature of Tb about 0.6 10^12 K. Its flux density and solid angle increased by a factor of about 2 during the period 1983.9 to 1990.8, but the birghtness temperature did not change significantly. The emission at millimeter wavelengths decreased by a factor of about 2 during the same period, while the UV emission from the nucleus also dcreased. We suggest that variations in the low-frequency emissions are caused by changes in the absorption by a cocoon - the thermal plasma surrounding the jet. The electron density in the region is Ne about 10^5 cm^-3and the longitudal field is about 40 microG. The emission measure and the rotation measure vary with r, the distance from the nucleus as r^-3. The data at lamda 49cm indi´cate several components in and near the "hotspot" at the end of the arcsec jet.

Nyckelord

galaxies:jets

radio continuum: galaxies

quasars: 3C345

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